diff --git a/src/audio-settings.c b/src/audio-settings.c
index ed3e7d16..5d590208 100644
--- a/src/audio-settings.c
+++ b/src/audio-settings.c
@@ -73,7 +73,7 @@ void ofono_audio_settings_mode_notify(struct ofono_audio_settings *as,
 	g_free(as->mode);
 	as->mode = g_strdup(mode);
 
-	if (!as->mode)
+	if (as->mode == NULL)
 		return;
 
 	ofono_dbus_signal_property_changed(conn, path,
@@ -89,7 +89,7 @@ static DBusMessage *audio_get_properties_reply(DBusMessage *msg,
 	DBusMessageIter dict;
 
 	reply = dbus_message_new_method_return(msg);
-	if (!reply)
+	if (reply == NULL)
 		return NULL;
 
 	dbus_message_iter_init_append(reply, &iter);
@@ -132,7 +132,7 @@ int ofono_audio_settings_driver_register(const struct ofono_audio_settings_drive
 {
 	DBG("driver: %p, name: %s", d, d->name);
 
-	if (!d->probe)
+	if (d->probe == NULL)
 		return -EINVAL;
 
 	g_drivers = g_slist_prepend(g_drivers, (void *) d);
@@ -164,7 +164,7 @@ static void audio_settings_remove(struct ofono_atom *atom)
 
 	DBG("atom: %p", atom);
 
-	if (!as)
+	if (as == NULL)
 		return;
 
 	if (as->driver && as->driver->remove)
@@ -182,11 +182,11 @@ struct ofono_audio_settings *ofono_audio_settings_create(struct ofono_modem *mod
 	struct ofono_audio_settings *as;
 	GSList *l;
 
-	if (!driver)
+	if (driver == NULL)
 		return NULL;
 
 	as = g_try_new0(struct ofono_audio_settings, 1);
-	if (!as)
+	if (as == NULL)
 		return NULL;
 
 	as->atom = __ofono_modem_add_atom(modem, OFONO_ATOM_TYPE_AUDIO_SETTINGS,
diff --git a/src/call-barring.c b/src/call-barring.c
index db32c0c3..bb155307 100644
--- a/src/call-barring.c
+++ b/src/call-barring.c
@@ -385,7 +385,7 @@ static gboolean cb_ss_control(int type, const char *sc,
 		type, sc, sia, sib, sic, dn);
 
 	fac = cb_ss_service_to_fac(sc);
-	if (!fac)
+	if (fac == NULL)
 		return FALSE;
 
 	cb_set_query_bounds(cb, fac, type == SS_CONTROL_TYPE_QUERY);
@@ -419,7 +419,7 @@ static gboolean cb_ss_control(int type, const char *sc,
 		break;
 	}
 
-	if (!operation) {
+	if (operation == NULL) {
 		reply = __ofono_error_not_implemented(msg);
 		g_dbus_send_message(conn, reply);
 
@@ -521,7 +521,7 @@ static gboolean cb_ss_passwd(const char *sc,
 	else
 		fac = cb_ss_service_to_fac(sc);
 
-	if (!fac)
+	if (fac == NULL)
 		return FALSE;
 
 	if (!is_valid_pin(old, PIN_TYPE_NET) || !is_valid_pin(new, PIN_TYPE_NET))
@@ -618,7 +618,7 @@ static void cb_get_properties_reply(struct ofono_call_barring *cb, int mask)
 		ofono_error("Generating a get_properties reply with no cache");
 
 	reply = dbus_message_new_method_return(cb->pending);
-	if (!reply)
+	if (reply == NULL)
 		return;
 
 	dbus_message_iter_init_append(reply, &iter);
@@ -678,7 +678,7 @@ static DBusMessage *cb_get_properties(DBusConnection *conn, DBusMessage *msg,
 	if (__ofono_call_barring_is_busy(cb) || __ofono_ussd_is_busy(cb->ussd))
 		return __ofono_error_busy(msg);
 
-	if (!cb->driver->query)
+	if (cb->driver->query == NULL)
 		return __ofono_error_not_implemented(msg);
 
 	cb->pending = dbus_message_ref(msg);
@@ -866,7 +866,7 @@ static DBusMessage *cb_set_property(DBusConnection *conn, DBusMessage *msg,
 			return __ofono_error_invalid_format(msg);
 	}
 
-	if (!cb->driver->set)
+	if (cb->driver->set == NULL)
 		return __ofono_error_not_implemented(msg);
 
 	cb_set_query_bounds(cb, cb_locks[lock].fac, FALSE);
@@ -899,7 +899,7 @@ static DBusMessage *cb_disable_all(DBusConnection *conn, DBusMessage *msg,
 	struct ofono_call_barring *cb = data;
 	const char *passwd;
 
-	if (!cb->driver->set)
+	if (cb->driver->set == NULL)
 		return __ofono_error_not_implemented(msg);
 
 	if (__ofono_call_barring_is_busy(cb) || __ofono_ussd_is_busy(cb->ussd))
@@ -946,7 +946,7 @@ static DBusMessage *cb_set_passwd(DBusConnection *conn, DBusMessage *msg,
 	const char *old_passwd;
 	const char *new_passwd;
 
-	if (!cb->driver->set_passwd)
+	if (cb->driver->set_passwd == NULL)
 		return __ofono_error_not_implemented(msg);
 
 	if (__ofono_call_barring_is_busy(cb) || __ofono_ussd_is_busy(cb->ussd))
@@ -1013,7 +1013,7 @@ static void call_barring_outgoing_enabled_notify(int idx, void *userdata)
 	signal = dbus_message_new_signal(path, OFONO_CALL_BARRING_INTERFACE,
 						"OutgoingBarringInEffect");
 
-	if (!signal) {
+	if (signal == NULL) {
 		ofono_error("Unable to allocate new %s.OutgoingBarringInEffect"
 				" signal", OFONO_CALL_BARRING_INTERFACE);
 		return;
diff --git a/src/call-forwarding.c b/src/call-forwarding.c
index ce03c402..bb8aa37f 100644
--- a/src/call-forwarding.c
+++ b/src/call-forwarding.c
@@ -113,7 +113,7 @@ static int cf_find_timeout(GSList *cf_list, int cls)
 	l = g_slist_find_custom(cf_list, GINT_TO_POINTER(cls),
 		cf_condition_find_with_cls);
 
-	if (!l)
+	if (l == NULL)
 		return DEFAULT_NO_REPLY_TIMEOUT;
 
 	c = l->data;
@@ -158,7 +158,7 @@ static GSList *cf_cond_list_create(int total,
 				continue;
 
 			cond = g_try_new0(struct ofono_call_forwarding_condition, 1);
-			if (!cond)
+			if (cond == NULL)
 				continue;
 
 			memcpy(cond, &list[i],
@@ -352,7 +352,7 @@ static void property_append_cf_conditions(DBusMessageIter *dict,
 		while (l && (cf = l->data) && (cf->cls < i))
 				l = l->next;
 
-		if (!l || cf->cls != i) {
+		if (l == NULL || cf->cls != i) {
 			property_append_cf_condition(dict, i, postfix, "",
 						DEFAULT_NO_REPLY_TIMEOUT);
 			continue;
@@ -374,8 +374,7 @@ static DBusMessage *cf_get_properties_reply(DBusMessage *msg,
 	int i;
 
 	reply = dbus_message_new_method_return(msg);
-
-	if (!reply)
+	if (reply == NULL)
 		return NULL;
 
 	dbus_message_iter_init_append(reply, &iter);
@@ -436,7 +435,7 @@ static DBusMessage *cf_get_properties(DBusConnection *conn, DBusMessage *msg,
 	if (cf->flags & CALL_FORWARDING_FLAG_CACHED)
 		return cf_get_properties_reply(msg, cf);
 
-	if (!cf->driver->query)
+	if (cf->driver->query == NULL)
 		return __ofono_error_not_implemented(msg);
 
 	if (__ofono_call_forwarding_is_busy(cf) ||
@@ -634,7 +633,7 @@ static DBusMessage *cf_set_property(DBusConnection *conn, DBusMessage *msg,
 				GINT_TO_POINTER(cls),
 				cf_condition_find_with_cls);
 
-		if (!l)
+		if (l == NULL)
 			return __ofono_error_failed(msg);
 
 		c = l->data;
@@ -713,7 +712,7 @@ static DBusMessage *cf_disable_all(DBusConnection *conn, DBusMessage *msg,
 	const char *strtype;
 	int type;
 
-	if (!cf->driver->erasure)
+	if (cf->driver->erasure == NULL)
 		return __ofono_error_not_implemented(msg);
 
 	if (__ofono_call_forwarding_is_busy(cf) ||
@@ -905,7 +904,7 @@ static gboolean cf_ss_control(int type, const char *sc,
 	void *operation = NULL;
 
 	/* Before we do anything, make sure we're actually initialized */
-	if (!cf)
+	if (cf == NULL)
 		return FALSE;
 
 	if (__ofono_call_forwarding_is_busy(cf)) {
@@ -1007,7 +1006,7 @@ static gboolean cf_ss_control(int type, const char *sc,
 		break;
 	}
 
-	if (!operation) {
+	if (operation == NULL) {
 		reply = __ofono_error_not_implemented(msg);
 		g_dbus_send_message(conn, reply);
 
@@ -1016,7 +1015,7 @@ static gboolean cf_ss_control(int type, const char *sc,
 
 	cf->ss_req = g_try_new0(struct cf_ss_request, 1);
 
-	if (!cf->ss_req) {
+	if (cf->ss_req == NULL) {
 		reply = __ofono_error_failed(msg);
 		g_dbus_send_message(conn, reply);
 
diff --git a/src/call-meter.c b/src/call-meter.c
index 568fe40f..ac3ae6b3 100644
--- a/src/call-meter.c
+++ b/src/call-meter.c
@@ -163,7 +163,7 @@ static void cm_get_properties_reply(struct ofono_call_meter *cm)
 	const char *currency = cm->currency;
 
 	reply = dbus_message_new_method_return(cm->pending);
-	if (!reply)
+	if (reply == NULL)
 		return;
 
 	dbus_message_iter_init_append(reply, &iter);
@@ -204,7 +204,7 @@ static void query_call_meter_callback(const struct ofono_error *error, int value
 
 static void query_call_meter(struct ofono_call_meter *cm)
 {
-	if (!cm->driver->call_meter_query) {
+	if (cm->driver->call_meter_query == NULL) {
 		if (cm->pending)
 			cm_get_properties_reply(cm);
 
@@ -227,7 +227,7 @@ static void query_acm_callback(const struct ofono_error *error, int value,
 
 static void query_acm(struct ofono_call_meter *cm)
 {
-	if (!cm->driver->acm_query) {
+	if (cm->driver->acm_query == NULL) {
 		query_call_meter(cm);
 		return;
 	}
@@ -250,7 +250,7 @@ static void query_acm_max_callback(const struct ofono_error *error, int value,
 
 static void query_acm_max(struct ofono_call_meter *cm)
 {
-	if (!cm->driver->acm_max_query) {
+	if (cm->driver->acm_max_query == NULL) {
 		cm->flags |= CALL_METER_FLAG_CACHED;
 
 		query_acm(cm);
@@ -276,7 +276,7 @@ static void query_puct_callback(const struct ofono_error *error,
 
 static void query_puct(struct ofono_call_meter *cm)
 {
-	if (!cm->driver->puct_query)
+	if (cm->driver->puct_query == NULL)
 		query_acm_max(cm);
 	else
 		cm->driver->puct_query(cm, query_puct_callback, cm);
@@ -312,7 +312,7 @@ static void set_acm_max_query_callback(const struct ofono_error *error, int valu
 	struct ofono_call_meter *cm = data;
 	DBusMessage *reply;
 
-	if (!cm->pending)
+	if (cm->pending == NULL)
 		return;
 
 	if (error->type != OFONO_ERROR_TYPE_NO_ERROR) {
@@ -353,7 +353,7 @@ static DBusMessage *prop_set_acm_max(DBusMessage *msg,
 {
 	dbus_uint32_t value;
 
-	if (!cm->driver->acm_max_set)
+	if (cm->driver->acm_max_set == NULL)
 		return __ofono_error_not_implemented(msg);
 
 	dbus_message_iter_get_basic(dbus_value, &value);
@@ -372,7 +372,7 @@ static void set_puct_query_callback(const struct ofono_error *error,
 	struct ofono_call_meter *cm = data;
 	DBusMessage *reply;
 
-	if (!cm->pending)
+	if (cm->pending == NULL)
 		return;
 
 	if (error->type != OFONO_ERROR_TYPE_NO_ERROR) {
@@ -421,7 +421,7 @@ static void set_puct_initial_query_callback(const struct ofono_error *error,
 	const char *name;
 	const char *pin2;
 
-	if (!cm->pending)
+	if (cm->pending == NULL)
 		return;
 
 	if (error->type != OFONO_ERROR_TYPE_NO_ERROR) {
@@ -456,7 +456,7 @@ static DBusMessage *prop_set_ppu(DBusMessage *msg, struct ofono_call_meter *cm,
 {
 	double ppu;
 
-	if (!cm->driver->puct_set || !cm->driver->puct_query)
+	if (cm->driver->puct_set == NULL || cm->driver->puct_query == NULL)
 		return __ofono_error_not_implemented(msg);
 
 	dbus_message_iter_get_basic(var, &ppu);
@@ -480,7 +480,7 @@ static DBusMessage *prop_set_cur(DBusMessage *msg, struct ofono_call_meter *cm,
 {
 	const char *value;
 
-	if (!cm->driver->puct_set || !cm->driver->puct_query)
+	if (cm->driver->puct_set == NULL || cm->driver->puct_query == NULL)
 		return __ofono_error_not_implemented(msg);
 
 	dbus_message_iter_get_basic(var, &value);
@@ -570,7 +570,7 @@ static void reset_acm_query_callback(const struct ofono_error *error, int value,
 	struct ofono_call_meter *cm = data;
 	DBusMessage *reply;
 
-	if (!cm->pending)
+	if (cm->pending == NULL)
 		return;
 
 	if (error->type != OFONO_ERROR_TYPE_NO_ERROR) {
@@ -610,7 +610,7 @@ static DBusMessage *cm_acm_reset(DBusConnection *conn, DBusMessage *msg,
 	struct ofono_call_meter *cm = data;
 	const char *pin2;
 
-	if (!cm->driver->acm_reset)
+	if (cm->driver->acm_reset == NULL)
 		return __ofono_error_not_implemented(msg);
 
 	if (cm->pending)
diff --git a/src/call-settings.c b/src/call-settings.c
index c6568336..49a7fb01 100644
--- a/src/call-settings.c
+++ b/src/call-settings.c
@@ -412,7 +412,7 @@ static gboolean cw_ss_control(int type,
 	int cls = BEARER_CLASS_SS_DEFAULT;
 	DBusMessage *reply;
 
-	if (!cs)
+	if (cs == NULL)
 		return FALSE;
 
 	if (strcmp(sc, "43"))
@@ -426,8 +426,8 @@ static gboolean cw_ss_control(int type,
 	if (strlen(sib) || strlen(sib) || strlen(dn))
 		goto bad_format;
 
-	if ((type == SS_CONTROL_TYPE_QUERY && !cs->driver->cw_query) ||
-		(type != SS_CONTROL_TYPE_QUERY && !cs->driver->cw_set)) {
+	if ((type == SS_CONTROL_TYPE_QUERY && cs->driver->cw_query == NULL) ||
+		(type != SS_CONTROL_TYPE_QUERY && cs->driver->cw_set == NULL)) {
 		reply = __ofono_error_not_implemented(msg);
 		goto error;
 	}
@@ -574,7 +574,7 @@ static gboolean clip_colp_colr_ss(int type,
 	void (*query_op)(struct ofono_call_settings *cs,
 				ofono_call_settings_status_cb_t cb, void *data);
 
-	if (!cs)
+	if (cs == NULL)
 		return FALSE;
 
 	if (__ofono_call_settings_is_busy(cs)) {
@@ -605,7 +605,7 @@ static gboolean clip_colp_colr_ss(int type,
 		return TRUE;
 	}
 
-	if (!query_op) {
+	if (query_op == NULL) {
 		DBusMessage *reply = __ofono_error_not_implemented(msg);
 		g_dbus_send_message(conn, reply);
 
@@ -694,7 +694,7 @@ static gboolean clir_ss_control(int type,
 	struct ofono_call_settings *cs = data;
 	DBusConnection *conn = ofono_dbus_get_connection();
 
-	if (!cs)
+	if (cs == NULL)
 		return FALSE;
 
 	if (strcmp(sc, "31"))
@@ -726,7 +726,7 @@ static gboolean clir_ss_control(int type,
 		return TRUE;
 	}
 
-	if (type != SS_CONTROL_TYPE_QUERY && !cs->driver->clir_set) {
+	if (type != SS_CONTROL_TYPE_QUERY && cs->driver->clir_set == NULL) {
 		DBusMessage *reply = __ofono_error_not_implemented(msg);
 		g_dbus_send_message(conn, reply);
 
@@ -799,8 +799,7 @@ static DBusMessage *generate_get_properties_reply(struct ofono_call_settings *cs
 	const char *str;
 
 	reply = dbus_message_new_method_return(msg);
-
-	if (!reply)
+	if (reply == NULL)
 		return NULL;
 
 	dbus_message_iter_init_append(reply, &iter);
@@ -859,7 +858,7 @@ out:
 
 static void query_clir(struct ofono_call_settings *cs)
 {
-	if (!cs->driver->clir_query) {
+	if (cs->driver->clir_query == NULL) {
 		if (cs->pending) {
 			DBusMessage *reply =
 				generate_get_properties_reply(cs,
@@ -886,7 +885,7 @@ static void cs_clip_callback(const struct ofono_error *error,
 
 static void query_clip(struct ofono_call_settings *cs)
 {
-	if (!cs->driver->clip_query) {
+	if (cs->driver->clip_query == NULL) {
 		query_clir(cs);
 		return;
 	}
@@ -907,7 +906,7 @@ static void cs_colp_callback(const struct ofono_error *error,
 
 static void query_colp(struct ofono_call_settings *cs)
 {
-	if (!cs->driver->colp_query) {
+	if (cs->driver->colp_query == NULL) {
 		query_clip(cs);
 		return;
 	}
@@ -928,7 +927,7 @@ static void cs_colr_callback(const struct ofono_error *error,
 
 static void query_colr(struct ofono_call_settings *cs)
 {
-	if (!cs->driver->colr_query) {
+	if (cs->driver->colr_query == NULL) {
 		query_colp(cs);
 		return;
 	}
@@ -949,7 +948,7 @@ static void cs_cw_callback(const struct ofono_error *error, int status,
 
 static void query_cw(struct ofono_call_settings *cs)
 {
-	if (!cs->driver->cw_query) {
+	if (cs->driver->cw_query == NULL) {
 		query_colr(cs);
 		return;
 	}
diff --git a/src/call-volume.c b/src/call-volume.c
index 6f692f32..1e12d810 100644
--- a/src/call-volume.c
+++ b/src/call-volume.c
@@ -236,7 +236,7 @@ static DBusMessage *cv_set_property(DBusConnection *conn, DBusMessage *msg,
 	if (g_str_equal(property, "SpeakerVolume") == TRUE) {
 		unsigned char percent;
 
-		if (!cv->driver->speaker_volume)
+		if (cv->driver->speaker_volume == NULL)
 			return __ofono_error_not_implemented(msg);
 
 		if (dbus_message_iter_get_arg_type(&var) != DBUS_TYPE_BYTE)
@@ -258,7 +258,7 @@ static DBusMessage *cv_set_property(DBusConnection *conn, DBusMessage *msg,
 	} else if (g_str_equal(property, "MicrophoneVolume") == TRUE) {
 		unsigned char percent;
 
-		if (!cv->driver->microphone_volume)
+		if (cv->driver->microphone_volume == NULL)
 			return __ofono_error_not_implemented(msg);
 
 		if (dbus_message_iter_get_arg_type(&var) != DBUS_TYPE_BYTE)
@@ -280,7 +280,7 @@ static DBusMessage *cv_set_property(DBusConnection *conn, DBusMessage *msg,
 	} else if (g_str_equal(property, "Muted") == TRUE) {
 		dbus_bool_t muted;
 
-		if (!cv->driver->mute)
+		if (cv->driver->mute == NULL)
 			return __ofono_error_not_implemented(msg);
 
 		if (dbus_message_iter_get_arg_type(&var) != DBUS_TYPE_BOOLEAN)
diff --git a/src/cbs.c b/src/cbs.c
index 50e78c29..8e4afc10 100644
--- a/src/cbs.c
+++ b/src/cbs.c
@@ -131,8 +131,7 @@ static void cbs_dispatch_emergency(struct ofono_cbs *cbs, const char *message,
 
 	signal = dbus_message_new_signal(path, OFONO_CELL_BROADCAST_INTERFACE,
 						"EmergencyBroadcast");
-
-	if (!signal)
+	if (signal == NULL)
 		return;
 
 	dbus_message_iter_init_append(signal, &iter);
@@ -195,7 +194,7 @@ void ofono_cbs_notify(struct ofono_cbs *cbs, const unsigned char *pdu,
 		struct ofono_atom *sim_atom;
 
 		sim_atom = __ofono_modem_find_atom(modem, OFONO_ATOM_TYPE_SIM);
-		if (!sim_atom)
+		if (sim_atom == NULL)
 			return;
 
 		if (!__ofono_sim_service_available(
@@ -289,8 +288,7 @@ static DBusMessage *cbs_get_properties(DBusConnection *conn,
 	char *topics;
 
 	reply = dbus_message_new_method_return(msg);
-
-	if (!reply)
+	if (reply == NULL)
 		return NULL;
 
 	dbus_message_iter_init_append(reply, &iter);
@@ -386,7 +384,7 @@ static DBusMessage *cbs_set_topics(struct ofono_cbs *cbs, const char *value,
 	if (topics == NULL && value[0] != '\0')
 		return __ofono_error_invalid_format(msg);
 
-	if (!cbs->driver->set_topics)
+	if (cbs->driver->set_topics == NULL)
 		return __ofono_error_not_implemented(msg);
 
 	cbs->new_topics = topics;
@@ -416,7 +414,7 @@ static void cbs_set_powered_cb(const struct ofono_error *error, void *data)
 	if (error->type != OFONO_ERROR_TYPE_NO_ERROR) {
 		ofono_error("Setting Cell Broadcast topics failed");
 
-		if (!cbs->pending)
+		if (cbs->pending == NULL)
 			return;
 
 		__ofono_dbus_pending_reply(&cbs->pending,
@@ -438,7 +436,7 @@ static void cbs_set_powered_cb(const struct ofono_error *error, void *data)
 						DBUS_TYPE_BOOLEAN,
 						&cbs->powered);
 
-	if (!cbs->pending)
+	if (cbs->pending == NULL)
 		return;
 
 	reply = dbus_message_new_method_return(cbs->pending);
@@ -455,7 +453,8 @@ static DBusMessage *cbs_set_powered(struct ofono_cbs *cbs, gboolean value,
 	if (cbs->powered == value)
 		goto reply;
 
-	if (!cbs->driver->set_topics || !cbs->driver->clear_topics)
+	if (cbs->driver->set_topics == NULL ||
+			cbs->driver->clear_topics == NULL)
 		goto done;
 
 	if (msg)
@@ -951,7 +950,7 @@ static void cbs_location_changed(int status, int lac, int ci, int tech,
 
 	DBG("%d, %d, %d, %d, %s%s", status, lac, ci, tech, mcc, mnc);
 
-	if (!mcc || !mnc) {
+	if (mcc == NULL || mnc == NULL) {
 		if (cbs->mcc[0] == '\0' && cbs->mnc[0] == '\0')
 			return;
 
diff --git a/src/common.c b/src/common.c
index f32153cb..5154b8d8 100644
--- a/src/common.c
+++ b/src/common.c
@@ -516,7 +516,7 @@ gboolean parse_ss_control_string(char *str, int *ss_type,
 	/* Must have at least one other '#' */
 	c = strrchr(str+cur, '#');
 
-	if (!c)
+	if (c == NULL)
 		goto out;
 
 	*dn = c+1;
diff --git a/src/dbus.c b/src/dbus.c
index ad292412..c24615f4 100644
--- a/src/dbus.c
+++ b/src/dbus.c
@@ -175,8 +175,7 @@ int ofono_dbus_signal_property_changed(DBusConnection *conn,
 	DBusMessageIter iter;
 
 	signal = dbus_message_new_signal(path, interface, "PropertyChanged");
-
-	if (!signal) {
+	if (signal == NULL) {
 		ofono_error("Unable to allocate new %s.PropertyChanged signal",
 				interface);
 		return -1;
@@ -202,8 +201,7 @@ int ofono_dbus_signal_array_property_changed(DBusConnection *conn,
 	DBusMessageIter iter;
 
 	signal = dbus_message_new_signal(path, interface, "PropertyChanged");
-
-	if (!signal) {
+	if (signal == NULL) {
 		ofono_error("Unable to allocate new %s.PropertyChanged signal",
 				interface);
 		return -1;
@@ -229,8 +227,7 @@ int ofono_dbus_signal_dict_property_changed(DBusConnection *conn,
 	DBusMessageIter iter;
 
 	signal = dbus_message_new_signal(path, interface, "PropertyChanged");
-
-	if (!signal) {
+	if (signal == NULL) {
 		ofono_error("Unable to allocate new %s.PropertyChanged signal",
 				interface);
 		return -1;
@@ -426,7 +423,7 @@ void __ofono_dbus_cleanup(void)
 {
 	DBusConnection *conn = ofono_dbus_get_connection();
 
-	if (!conn || !dbus_connection_get_is_connected(conn))
+	if (conn == NULL || !dbus_connection_get_is_connected(conn))
 		return;
 
 	dbus_gsm_set_connection(NULL);
diff --git a/src/gprs.c b/src/gprs.c
index 7e42a99c..610f3b23 100644
--- a/src/gprs.c
+++ b/src/gprs.c
@@ -336,7 +336,7 @@ static void pri_context_signal_settings(struct pri_context *ctx)
 					OFONO_CONNECTION_CONTEXT_INTERFACE,
 					"PropertyChanged");
 
-	if (!signal)
+	if (signal == NULL)
 		return;
 
 	dbus_message_iter_init_append(signal, &iter);
@@ -400,7 +400,7 @@ static void pri_ifupdown(const char *interface, ofono_bool_t active)
 	struct ifreq ifr;
 	int sk;
 
-	if (!interface)
+	if (interface == NULL)
 		return;
 
 	sk = socket(PF_INET, SOCK_DGRAM, 0);
@@ -436,7 +436,7 @@ static void pri_setaddr(const char *interface, const char *address)
 	struct sockaddr_in addr;
 	int sk;
 
-	if (!interface)
+	if (interface == NULL)
 		return;
 
 	sk = socket(PF_INET, SOCK_DGRAM, 0);
@@ -459,7 +459,7 @@ static void pri_setaddr(const char *interface, const char *address)
 		goto done;
 	}
 
-	if (!address)
+	if (address == NULL)
 		goto done;
 
 	memset(&addr, 0, sizeof(addr));
@@ -480,7 +480,7 @@ static void pri_setproxy(const char *interface, const char *proxy)
 	struct sockaddr_in addr;
 	int sk;
 
-	if (!interface)
+	if (interface == NULL)
 		return;
 
 	sk = socket(PF_INET, SOCK_DGRAM, 0);
@@ -550,7 +550,7 @@ static void pri_update_context_settings(struct pri_context *ctx,
 		context_settings_free(ctx->settings);
 
 	ctx->settings = g_try_new0(struct context_settings, 1);
-	if (!ctx->settings)
+	if (ctx->settings == NULL)
 		return;
 
 	ctx->settings->type = ctx->type;
@@ -633,7 +633,7 @@ static DBusMessage *pri_get_properties(DBusConnection *conn,
 	DBusMessageIter dict;
 
 	reply = dbus_message_new_method_return(msg);
-	if (!reply)
+	if (reply == NULL)
 		return NULL;
 
 	dbus_message_iter_init_append(reply, &iter);
@@ -1147,12 +1147,12 @@ static struct pri_context *pri_context_create(struct ofono_gprs *gprs,
 {
 	struct pri_context *context = g_try_new0(struct pri_context, 1);
 
-	if (!context)
+	if (context == NULL)
 		return NULL;
 
-	if (!name) {
+	if (name == NULL) {
 		name = gprs_context_default_name(type);
-		if (!name)
+		if (name == NULL)
 			return NULL;
 	}
 
@@ -1419,7 +1419,7 @@ static DBusMessage *gprs_get_properties(DBusConnection *conn,
 	dbus_bool_t value;
 
 	reply = dbus_message_new_method_return(msg);
-	if (!reply)
+	if (reply == NULL)
 		return NULL;
 
 	dbus_message_iter_init_append(reply, &iter);
@@ -1497,7 +1497,7 @@ static DBusMessage *gprs_set_property(DBusConnection *conn,
 
 		gprs_netreg_update(gprs);
 	} else if (!strcmp(property, "Powered")) {
-		if (!gprs->driver->set_attached)
+		if (gprs->driver->set_attached == NULL)
 			return __ofono_error_not_implemented(msg);
 
 		if (dbus_message_iter_get_arg_type(&var) != DBUS_TYPE_BOOLEAN)
@@ -1563,7 +1563,7 @@ static struct pri_context *add_context(struct ofono_gprs *gprs,
 		return NULL;
 
 	context = pri_context_create(gprs, name, type);
-	if (!context) {
+	if (context == NULL) {
 		ofono_error("Unable to allocate context struct");
 		return NULL;
 	}
@@ -1709,7 +1709,7 @@ static DBusMessage *gprs_remove_context(DBusConnection *conn,
 		return __ofono_error_invalid_format(msg);
 
 	ctx = gprs_context_by_path(gprs, path);
-	if (!ctx)
+	if (ctx == NULL)
 		return __ofono_error_not_found(msg);
 
 	if (ctx->active) {
diff --git a/src/history.c b/src/history.c
index 7d3c9278..3eb9a3da 100644
--- a/src/history.c
+++ b/src/history.c
@@ -105,8 +105,7 @@ void __ofono_history_probe_drivers(struct ofono_modem *modem)
 		driver = l->data;
 
 		context = history_context_create(modem, driver);
-
-		if (!context)
+		if (context == NULL)
 			continue;
 
 		__ofono_modem_add_atom(modem, OFONO_ATOM_TYPE_HISTORY,
diff --git a/src/main.c b/src/main.c
index eca008ed..87fb0ab8 100644
--- a/src/main.c
+++ b/src/main.c
@@ -214,7 +214,7 @@ int main(int argc, char **argv)
 	dbus_error_init(&error);
 
 	conn = g_dbus_setup_bus(DBUS_BUS_SYSTEM, OFONO_SERVICE, &error);
-	if (!conn) {
+	if (conn == NULL) {
 		if (dbus_error_is_set(&error) == TRUE) {
 			ofono_error("Unable to hop onto D-Bus: %s",
 					error.message);
diff --git a/src/message-waiting.c b/src/message-waiting.c
index 97a238c0..d8bfe34b 100644
--- a/src/message-waiting.c
+++ b/src/message-waiting.c
@@ -119,7 +119,7 @@ static DBusMessage *mw_get_properties(DBusConnection *conn,
 	const char *number;
 
 	reply = dbus_message_new_method_return(msg);
-	if (!reply)
+	if (reply == NULL)
 		return NULL;
 
 	dbus_message_iter_init_append(reply, &iter);
@@ -395,7 +395,7 @@ static void update_indicator_and_emit(struct ofono_message_waiting *mw,
 	indication = info->indication;
 	count = info->message_count;
 
-	if (!mw_message_waiting_property_name[mailbox])
+	if (mw_message_waiting_property_name[mailbox] == NULL)
 		return;
 
 	ofono_dbus_signal_property_changed(conn, path,
diff --git a/src/modem.c b/src/modem.c
index f032d93c..52e647ba 100644
--- a/src/modem.c
+++ b/src/modem.c
@@ -532,7 +532,7 @@ static DBusMessage *set_property_online(struct ofono_modem *modem,
 	if (modem->pending != NULL)
 		return __ofono_error_busy(msg);
 
-	if (!driver->set_online)
+	if (driver->set_online == NULL)
 		return __ofono_error_not_implemented(msg);
 
 	if (modem->modem_state < MODEM_STATE_OFFLINE)
@@ -628,7 +628,7 @@ static DBusMessage *modem_get_properties(DBusConnection *conn,
 	DBusMessageIter dict;
 
 	reply = dbus_message_new_method_return(msg);
-	if (!reply)
+	if (reply == NULL)
 		return NULL;
 
 	dbus_message_iter_init_append(reply, &iter);
@@ -947,7 +947,7 @@ void ofono_modem_remove_interface(struct ofono_modem *modem,
 
 	found = g_slist_find_custom(modem->interface_list, interface,
 						(GCompareFunc) strcmp);
-	if (!found) {
+	if (found == NULL) {
 		ofono_error("Interface %s not found on the interface_list",
 				interface);
 		return;
@@ -994,7 +994,7 @@ static void query_serial_cb(const struct ofono_error *error,
 
 static void query_serial(struct ofono_devinfo *info)
 {
-	if (!info->driver->query_serial)
+	if (info->driver->query_serial == NULL)
 		return;
 
 	info->driver->query_serial(info, query_serial_cb, info);
@@ -1023,7 +1023,7 @@ out:
 
 static void query_revision(struct ofono_devinfo *info)
 {
-	if (!info->driver->query_revision) {
+	if (info->driver->query_revision == NULL) {
 		query_serial(info);
 		return;
 	}
@@ -1054,7 +1054,7 @@ out:
 
 static void query_model(struct ofono_devinfo *info)
 {
-	if (!info->driver->query_model) {
+	if (info->driver->query_model == NULL) {
 		/* If model is not supported, don't bother querying revision */
 		query_serial(info);
 	}
@@ -1088,7 +1088,7 @@ static gboolean query_manufacturer(gpointer user)
 {
 	struct ofono_devinfo *info = user;
 
-	if (!info->driver->query_manufacturer) {
+	if (info->driver->query_manufacturer == NULL) {
 		query_model(info);
 		return FALSE;
 	}
diff --git a/src/nettime.c b/src/nettime.c
index 904deeef..06242596 100644
--- a/src/nettime.c
+++ b/src/nettime.c
@@ -77,8 +77,7 @@ void __ofono_nettime_probe_drivers(struct ofono_modem *modem)
 		driver = l->data;
 
 		context = nettime_context_create(modem, driver);
-
-		if (!context)
+		if (context == NULL)
 			continue;
 
 		__ofono_modem_add_atom(modem, OFONO_ATOM_TYPE_NETTIME,
diff --git a/src/network.c b/src/network.c
index 83014bbe..d5b42a1c 100644
--- a/src/network.c
+++ b/src/network.c
@@ -194,7 +194,7 @@ static void register_callback(const struct ofono_error *error, void *data)
 	DBusConnection *conn = ofono_dbus_get_connection();
 	DBusMessage *reply;
 
-	if (!netreg->pending)
+	if (netreg->pending == NULL)
 		goto out;
 
 	if (error->type == OFONO_ERROR_TYPE_NO_ERROR)
@@ -352,7 +352,7 @@ static char *get_operator_display_name(struct ofono_netreg *netreg)
 	 * together there are four cases to consider.
 	 */
 
-	if (!opd) {
+	if (opd == NULL) {
 		g_strlcpy(name, "", len);
 		return name;
 	}
@@ -371,7 +371,7 @@ static char *get_operator_display_name(struct ofono_netreg *netreg)
 	if (opd->eons_info && opd->eons_info->longname)
 		plmn = opd->eons_info->longname;
 
-	if (!netreg->spname || strlen(netreg->spname) == 0) {
+	if (netreg->spname == NULL || strlen(netreg->spname) == 0) {
 		g_strlcpy(name, plmn, len);
 		return name;
 	}
@@ -458,7 +458,7 @@ static void set_network_operator_eons_info(struct network_operator_data *opd,
 	const char *oldinfo;
 	const char *newinfo;
 
-	if (!old_eons_info && !eons_info)
+	if (old_eons_info == NULL && eons_info == NULL)
 		return;
 
 	path = network_operator_build_path(netreg, opd->mcc, opd->mnc);
@@ -566,7 +566,7 @@ static DBusMessage *network_operator_get_properties(DBusConnection *conn,
 	DBusMessageIter iter;
 	DBusMessageIter dict;
 	reply = dbus_message_new_method_return(msg);
-	if (!reply)
+	if (reply == NULL)
 		return NULL;
 
 	dbus_message_iter_init_append(reply, &iter);
@@ -671,7 +671,7 @@ static GSList *compress_operator_list(const struct ofono_network_operator *list,
 			o = g_slist_find_custom(oplist, &list[i],
 						network_operator_compare);
 
-		if (!o) {
+		if (o == NULL) {
 			opd = network_operator_create(&list[i]);
 			oplist = g_slist_prepend(oplist, opd);
 		} else if (o && list[i].tech != -1) {
@@ -760,7 +760,7 @@ static DBusMessage *network_get_properties(DBusConnection *conn,
 	const char *mode = registration_mode_to_string(netreg->mode);
 
 	reply = dbus_message_new_method_return(msg);
-	if (!reply)
+	if (reply == NULL)
 		return NULL;
 
 	dbus_message_iter_init_append(reply, &iter);
@@ -1217,7 +1217,7 @@ static void current_operator_callback(const struct ofono_error *error,
 		return;
 	}
 
-	if (!netreg->current_operator && !current)
+	if (netreg->current_operator == NULL && current == NULL)
 		return;
 
 	/* We got a new network operator, reset the previous one's status */
@@ -1299,7 +1299,7 @@ emit:
 void ofono_netreg_status_notify(struct ofono_netreg *netreg, int status,
 			int lac, int ci, int tech)
 {
-	if (!netreg)
+	if (netreg == NULL)
 		return;
 
 	if (netreg->status != status)
@@ -1339,7 +1339,7 @@ void ofono_netreg_time_notify(struct ofono_netreg *netreg,
 {
 	struct ofono_modem *modem = __ofono_atom_get_modem(netreg->atom);
 
-	if (!info)
+	if (info == NULL)
 		return;
 
 	__ofono_nettime_info_received(modem, info);
@@ -1465,7 +1465,7 @@ static void sim_pnn_read_cb(int ok, int length, int record,
 
 	total = length / record_length;
 
-	if (!netreg->eons)
+	if (netreg->eons == NULL)
 		netreg->eons = sim_eons_new(total);
 
 	sim_eons_add_pnn_record(netreg->eons, record, data, record_length);
@@ -1498,7 +1498,7 @@ static void sim_spdi_read_cb(int ok, int length, int record,
 
 	netreg->spdi = sim_spdi_new(data, length);
 
-	if (!current)
+	if (current == NULL)
 		return;
 
 	if (netreg->status == NETWORK_REGISTRATION_STATUS_ROAMING) {
@@ -1549,8 +1549,7 @@ static void sim_spn_read_cb(int ok, int length, int record,
 	 * paragraph as 51.101 and has an Annex B which we implement.
 	 */
 	spn = sim_string_to_utf8(data + 1, length - 1);
-
-	if (!spn) {
+	if (spn == NULL) {
 		ofono_error("EFspn read successfully, but couldn't parse");
 		return;
 	}
@@ -1772,8 +1771,7 @@ static void netreg_load_settings(struct ofono_netreg *netreg)
 	int mode;
 
 	imsi = ofono_sim_get_imsi(netreg->sim);
-
-	if (!imsi)
+	if (imsi == NULL)
 		return;
 
 	netreg->settings = storage_open(imsi, SETTINGS_STORE);
diff --git a/src/phonebook.c b/src/phonebook.c
index cae2b14c..e388ac1e 100644
--- a/src/phonebook.c
+++ b/src/phonebook.c
@@ -155,7 +155,7 @@ static void vcard_printf_number(GString *vcards, const char *number, int type,
 	char *pref = "", *intl = "", *category_string = "";
 	char buf[128];
 
-	if (!number || !strlen(number) || !type)
+	if (number == NULL || !strlen(number) || !type)
 		return;
 
 	switch (category) {
@@ -277,8 +277,7 @@ static DBusMessage *generate_export_entries_reply(struct ofono_phonebook *pb,
 	DBusMessageIter iter;
 
 	reply = dbus_message_new_method_return(msg);
-
-	if (!reply)
+	if (reply == NULL)
 		return NULL;
 
 	dbus_message_iter_init_append(reply, &iter);
@@ -292,7 +291,7 @@ static gboolean need_merge(const char *text)
 	int len;
 	char c;
 
-	if (!text)
+	if (text == NULL)
 		return FALSE;
 
 	len = strlen(text);
@@ -375,7 +374,7 @@ void ofono_phonebook_entry(struct ofono_phonebook *phonebook, int index,
 				break;
 		}
 
-		if (!l) {
+		if (l == NULL) {
 			person = g_new0(struct phonebook_person, 1);
 			phonebook->merge_list =
 				g_slist_prepend(phonebook->merge_list, person);
@@ -444,8 +443,7 @@ static void export_phonebook(struct ofono_phonebook *phonebook)
 	}
 
 	reply = generate_export_entries_reply(phonebook, phonebook->pending);
-
-	if (!reply) {
+	if (reply == NULL) {
 		dbus_message_unref(phonebook->pending);
 		return;
 	}
diff --git a/src/plugin.c b/src/plugin.c
index 7c0652bb..25e9a5a2 100644
--- a/src/plugin.c
+++ b/src/plugin.c
@@ -88,7 +88,7 @@ static gboolean check_plugin(struct ofono_plugin_desc *desc,
 		for (; *patterns; patterns++)
 			if (g_pattern_match_simple(*patterns, desc->name))
 				break;
-		if (!*patterns) {
+		if (*patterns == NULL) {
 			ofono_info("Ignoring %s", desc->description);
 			return FALSE;
 		}
diff --git a/src/radio-settings.c b/src/radio-settings.c
index 5794221f..ff6934b4 100644
--- a/src/radio-settings.c
+++ b/src/radio-settings.c
@@ -96,7 +96,7 @@ static DBusMessage *radio_get_properties_reply(DBusMessage *msg,
 	const char *mode = radio_access_mode_to_string(rs->mode);
 
 	reply = dbus_message_new_method_return(msg);
-	if (!reply)
+	if (reply == NULL)
 		return NULL;
 
 	dbus_message_iter_init_append(reply, &iter);
@@ -233,7 +233,7 @@ static void radio_fast_dormancy_query_callback(const struct ofono_error *error,
 
 static void radio_query_fast_dormancy(struct ofono_radio_settings *rs)
 {
-	if (!rs->driver->query_fast_dormancy) {
+	if (rs->driver->query_fast_dormancy == NULL) {
 		radio_send_properties_reply(rs);
 		return;
 	}
@@ -270,7 +270,7 @@ static DBusMessage *radio_get_properties(DBusConnection *conn,
 	if (rs->flags & RADIO_SETTINGS_FLAG_CACHED)
 		return radio_get_properties_reply(msg, rs);
 
-	if (!rs->driver->query_rat_mode)
+	if (rs->driver->query_rat_mode == NULL)
 		return __ofono_error_not_implemented(msg);
 
 	if (rs->pending)
@@ -311,7 +311,7 @@ static DBusMessage *radio_set_property(DBusConnection *conn, DBusMessage *msg,
 		const char *value;
 		enum ofono_radio_access_mode mode;
 
-		if (!rs->driver->set_rat_mode)
+		if (rs->driver->set_rat_mode == NULL)
 			return __ofono_error_not_implemented(msg);
 
 		if (dbus_message_iter_get_arg_type(&var) != DBUS_TYPE_STRING)
@@ -334,7 +334,7 @@ static DBusMessage *radio_set_property(DBusConnection *conn, DBusMessage *msg,
 		dbus_bool_t value;
 		int target;
 
-		if (!rs->driver->set_fast_dormancy)
+		if (rs->driver->set_fast_dormancy == NULL)
 			return __ofono_error_not_implemented(msg);
 
 		if (dbus_message_iter_get_arg_type(&var) != DBUS_TYPE_BOOLEAN)
@@ -374,7 +374,7 @@ int ofono_radio_settings_driver_register(const struct ofono_radio_settings_drive
 {
 	DBG("driver: %p, name: %s", d, d->name);
 
-	if (!d || !d->probe)
+	if (d == NULL || d->probe == NULL)
 		return -EINVAL;
 
 	g_drivers = g_slist_prepend(g_drivers, (void *) d);
@@ -386,7 +386,7 @@ void ofono_radio_settings_driver_unregister(const struct ofono_radio_settings_dr
 {
 	DBG("driver: %p, name: %s", d, d->name);
 
-	if (!d)
+	if (d == NULL)
 		return;
 
 	g_drivers = g_slist_remove(g_drivers, (void *) d);
@@ -409,7 +409,7 @@ static void radio_settings_remove(struct ofono_atom *atom)
 
 	DBG("atom: %p", atom);
 
-	if (!rs)
+	if (rs == NULL)
 		return;
 
 	if (rs->driver && rs->driver->remove)
@@ -426,11 +426,11 @@ struct ofono_radio_settings *ofono_radio_settings_create(struct ofono_modem *mod
 	struct ofono_radio_settings *rs;
 	GSList *l;
 
-	if (!driver)
+	if (driver == NULL)
 		return NULL;
 
 	rs = g_try_new0(struct ofono_radio_settings, 1);
-	if (!rs)
+	if (rs == NULL)
 		return NULL;
 
 	rs->mode = -1;
diff --git a/src/sim.c b/src/sim.c
index bc7859c6..860f1790 100644
--- a/src/sim.c
+++ b/src/sim.c
@@ -292,7 +292,7 @@ static DBusMessage *sim_get_properties(DBusConnection *conn,
 	dbus_bool_t bdn;
 
 	reply = dbus_message_new_method_return(msg);
-	if (!reply)
+	if (reply == NULL)
 		return NULL;
 
 	dbus_message_iter_init_append(reply, &iter);
@@ -582,7 +582,7 @@ static DBusMessage *sim_lock_or_unlock(struct ofono_sim *sim, int lock,
 	const char *typestr;
 	const char *pin;
 
-	if (!sim->driver->lock)
+	if (sim->driver->lock == NULL)
 		return __ofono_error_not_implemented(msg);
 
 	if (sim->pending)
@@ -653,7 +653,7 @@ static DBusMessage *sim_change_pin(DBusConnection *conn, DBusMessage *msg,
 	const char *old;
 	const char *new;
 
-	if (!sim->driver->change_passwd)
+	if (sim->driver->change_passwd == NULL)
 		return __ofono_error_not_implemented(msg);
 
 	if (sim->pending)
@@ -709,7 +709,7 @@ static DBusMessage *sim_enter_pin(DBusConnection *conn, DBusMessage *msg,
 	enum ofono_sim_password_type type;
 	const char *pin;
 
-	if (!sim->driver->send_passwd)
+	if (sim->driver->send_passwd == NULL)
 		return __ofono_error_not_implemented(msg);
 
 	if (sim->pending)
@@ -918,7 +918,7 @@ static DBusMessage *sim_reset_pin(DBusConnection *conn, DBusMessage *msg,
 	const char *puk;
 	const char *pin;
 
-	if (!sim->driver->reset_passwd)
+	if (sim->driver->reset_passwd == NULL)
 		return __ofono_error_not_implemented(msg);
 
 	if (sim->pending)
@@ -976,7 +976,7 @@ static gboolean numbers_list_equal(GSList *a, GSList *b)
 	struct ofono_phone_number *num_a, *num_b;
 
 	while (a || b) {
-		if (!a || !b)
+		if (a == NULL || b == NULL)
 			return FALSE;
 
 		num_a = a->data;
@@ -1242,7 +1242,7 @@ static void sim_imsi_cb(const struct ofono_error *error, const char *imsi,
 
 static void sim_retrieve_imsi(struct ofono_sim *sim)
 {
-	if (!sim->driver->read_imsi) {
+	if (sim->driver->read_imsi == NULL) {
 		ofono_error("IMSI retrieval not implemented,"
 				" only emergency calls will be available");
 		return;
@@ -1592,7 +1592,7 @@ checkdone:
 
 static void sim_pin_check(struct ofono_sim *sim)
 {
-	if (!sim->driver->query_passwd_state) {
+	if (sim->driver->query_passwd_state == NULL) {
 		sim_initialize_after_pin(sim);
 		return;
 	}
diff --git a/src/sms.c b/src/sms.c
index 12988c8d..7da66c61 100644
--- a/src/sms.c
+++ b/src/sms.c
@@ -191,11 +191,11 @@ static unsigned int add_sms_handler(struct ofono_watchlist *watchlist,
 {
 	struct sms_handler *handler;
 
-	if (!notify)
+	if (notify == NULL)
 		return 0;
 
 	handler = g_try_new0(struct sms_handler, 1);
-	if (!handler)
+	if (handler == NULL)
 		return 0;
 
 	handler->dst = dst;
@@ -212,7 +212,7 @@ unsigned int __ofono_sms_text_watch_add(struct ofono_sms *sms,
 					ofono_sms_text_notify_cb_t cb,
 					void *data, ofono_destroy_func destroy)
 {
-	if (!sms)
+	if (sms == NULL)
 		return 0;
 
 	DBG("%p", sms);
@@ -223,7 +223,7 @@ unsigned int __ofono_sms_text_watch_add(struct ofono_sms *sms,
 gboolean __ofono_sms_text_watch_remove(struct ofono_sms *sms,
 					unsigned int id)
 {
-	if (!sms)
+	if (sms == NULL)
 		return FALSE;
 
 	DBG("%p", sms);
@@ -236,7 +236,7 @@ unsigned int __ofono_sms_datagram_watch_add(struct ofono_sms *sms,
 					int dst, int src, void *data,
 					ofono_destroy_func destroy)
 {
-	if (!sms)
+	if (sms == NULL)
 		return 0;
 
 	DBG("%p: dst %d, src %d", sms, dst, src);
@@ -248,7 +248,7 @@ unsigned int __ofono_sms_datagram_watch_add(struct ofono_sms *sms,
 gboolean __ofono_sms_datagram_watch_remove(struct ofono_sms *sms,
 					unsigned int id)
 {
-	if (!sms)
+	if (sms == NULL)
 		return FALSE;
 
 	DBG("%p", sms);
@@ -265,8 +265,7 @@ static DBusMessage *message_get_properties(DBusConnection *conn,
 	DBusMessageIter dict;
 
 	reply = dbus_message_new_method_return(msg);
-
-	if (!reply)
+	if (reply == NULL)
 		return NULL;
 
 	dbus_message_iter_init_append(reply, &iter);
@@ -330,7 +329,7 @@ static gboolean message_dbus_register(struct ofono_sms *sms, struct message *m)
 	DBusConnection *conn = ofono_dbus_get_connection();
 	const char *path;
 
-	if (!m)
+	if (m == NULL)
 		return FALSE;
 
 	path = __ofono_sms_message_path_from_uuid(sms, &m->uuid);
@@ -486,8 +485,7 @@ static DBusMessage *generate_get_properties_reply(struct ofono_sms *sms,
 	const char *bearer;
 
 	reply = dbus_message_new_method_return(msg);
-
-	if (!reply)
+	if (reply == NULL)
 		return NULL;
 
 	dbus_message_iter_init_append(reply, &iter);
@@ -541,7 +539,7 @@ static DBusMessage *sms_get_properties(DBusConnection *conn,
 	if (sms->pending)
 		return __ofono_error_busy(msg);
 
-	if (!sms->driver->sca_query)
+	if (sms->driver->sca_query == NULL)
 		return __ofono_error_not_implemented(msg);
 
 	if (sms->flags & MESSAGE_MANAGER_FLAG_CACHED)
@@ -832,7 +830,7 @@ static gboolean tx_next(gpointer user_data)
 
 	sms->tx_source = 0;
 
-	if (!entry)
+	if (entry == NULL)
 		return FALSE;
 
 	if (g_queue_get_length(sms->txq) > 1
@@ -991,7 +989,7 @@ static DBusMessage *sms_send_message(DBusConnection *conn, DBusMessage *msg,
 	msg_list = sms_text_prepare(to, text, sms->ref, use_16bit_ref,
 						sms->use_delivery_reports);
 
-	if (!msg_list)
+	if (msg_list == NULL)
 		return __ofono_error_invalid_format(msg);
 
 	flags = OFONO_SMS_SUBMIT_FLAG_RECORD_HISTORY;
@@ -1175,7 +1173,7 @@ static void dispatch_text_message(struct ofono_sms *sms,
 	struct sms_handler *h;
 	GSList *l;
 
-	if (!message)
+	if (message == NULL)
 		return;
 
 	if (cls == SMS_CLASS_0)
@@ -1186,7 +1184,7 @@ static void dispatch_text_message(struct ofono_sms *sms,
 	signal = dbus_message_new_signal(path, OFONO_MESSAGE_MANAGER_INTERFACE,
 						signal_name);
 
-	if (!signal)
+	if (signal == NULL)
 		return;
 
 	dbus_message_iter_init_append(signal, &iter);
@@ -1324,8 +1322,7 @@ static void sms_dispatch(struct ofono_sms *sms, GSList *sms_list)
 		}
 
 		buf = sms_decode_datagram(sms_list, &len);
-
-		if (!buf)
+		if (buf == NULL)
 			return;
 
 		dispatch_app_datagram(sms, &uuid, dstport, srcport, buf, len,
@@ -1335,7 +1332,7 @@ static void sms_dispatch(struct ofono_sms *sms, GSList *sms_list)
 	} else {
 		char *message = sms_decode_text(sms_list);
 
-		if (!message)
+		if (message == NULL)
 			return;
 
 		dispatch_text_message(sms, &uuid, message, cls,
@@ -1357,7 +1354,7 @@ static void handle_deliver(struct ofono_sms *sms, const struct sms *incoming)
 	if (sms_extract_concatenation(incoming, &ref, &max, &seq)) {
 		GSList *sms_list;
 
-		if (!sms->assembly)
+		if (sms->assembly == NULL)
 			return;
 
 		sms_list = sms_assembly_add_fragment(sms->assembly,
@@ -1365,7 +1362,7 @@ static void handle_deliver(struct ofono_sms *sms, const struct sms *incoming)
 						&incoming->deliver.oaddr,
 						ref, max, seq);
 
-		if (!sms_list)
+		if (sms_list == NULL)
 			return;
 
 		sms_dispatch(sms, sms_list);
@@ -1489,7 +1486,7 @@ void ofono_sms_deliver_notify(struct ofono_sms *sms, unsigned char *pdu,
 
 		sim_atom = __ofono_modem_find_atom(modem, OFONO_ATOM_TYPE_SIM);
 
-		if (!sim_atom)
+		if (sim_atom == NULL)
 			return;
 
 		if (!__ofono_sim_service_available(
@@ -1500,7 +1497,7 @@ void ofono_sms_deliver_notify(struct ofono_sms *sms, unsigned char *pdu,
 
 		stk_atom = __ofono_modem_find_atom(modem, OFONO_ATOM_TYPE_STK);
 
-		if (!stk_atom)
+		if (stk_atom == NULL)
 			return;
 
 		__ofono_sms_sim_download(__ofono_atom_get_data(stk_atom),
diff --git a/src/smsagent.c b/src/smsagent.c
index bb0a3abd..9d6f21da 100644
--- a/src/smsagent.c
+++ b/src/smsagent.c
@@ -63,7 +63,7 @@ static struct sms_agent_request *sms_agent_request_new(struct sms_agent *agent,
 	struct sms_agent_request *req;
 
 	req = g_try_new0(struct sms_agent_request, 1);
-	if (!req)
+	if (req == NULL)
 		return NULL;
 
 	req->agent = agent;
@@ -99,7 +99,7 @@ static void sms_agent_send_noreply(struct sms_agent *agent, const char *method)
 
 	message = dbus_message_new_method_call(agent->service, agent->path,
 						agent->interface, method);
-	if (!message)
+	if (message == NULL)
 		return;
 
 	dbus_message_set_no_reply(message, TRUE);
@@ -130,7 +130,7 @@ struct sms_agent *sms_agent_new(const char *interface,
 	struct sms_agent *agent = g_try_new0(struct sms_agent, 1);
 	DBusConnection *conn = ofono_dbus_get_connection();
 
-	if (!agent)
+	if (agent == NULL)
 		return NULL;
 
 	agent->interface = g_strdup(interface);
@@ -164,7 +164,7 @@ void sms_agent_free(struct sms_agent *agent)
 {
 	DBusConnection *conn = ofono_dbus_get_connection();
 
-	if (!agent)
+	if (agent == NULL)
 		return;
 
 	if (agent->disconnect_watch) {
@@ -266,12 +266,12 @@ int sms_agent_dispatch_datagram(struct sms_agent *agent, const char *method,
 	const char *str = buf;
 
 	req = sms_agent_request_new(agent, cb, user_data, destroy);
-	if (!req)
+	if (req == NULL)
 		return -ENOMEM;
 
 	req->msg = dbus_message_new_method_call(agent->service, agent->path,
 						agent->interface, method);
-	if (!req->msg) {
+	if (req->msg == NULL) {
 		sms_agent_request_free(req);
 		return -ENOMEM;
 	}
diff --git a/src/stk.c b/src/stk.c
index 88b162c1..a4abb7d3 100644
--- a/src/stk.c
+++ b/src/stk.c
@@ -116,7 +116,7 @@ static int stk_respond(struct ofono_stk *stk, struct stk_response *rsp,
 	rsp->qualifier = stk->pending_cmd->qualifier;
 
 	tlv = stk_pdu_from_response(rsp, &tlv_len);
-	if (!tlv)
+	if (tlv == NULL)
 		return -EINVAL;
 
 	stk_command_free(stk->pending_cmd);
@@ -208,7 +208,7 @@ static int stk_send_envelope(struct ofono_stk *stk, struct stk_envelope *e,
 
 	e->dst = STK_DEVICE_IDENTITY_TYPE_UICC;
 	tlv = stk_pdu_from_envelope(e, &tlv_len);
-	if (!tlv)
+	if (tlv == NULL)
 		return -EINVAL;
 
 	op = g_new0(struct envelope_op, 1);
@@ -342,7 +342,7 @@ static struct stk_menu *stk_menu_create(const char *title,
 
 	ret->title = dbus_apply_text_attributes(title ? title : "",
 						title_attr);
-	if (!ret->title)
+	if (ret->title == NULL)
 		ret->title = g_strdup(title ? title : "");
 
 	memcpy(&ret->icon, icon, sizeof(ret->icon));
@@ -366,7 +366,7 @@ static struct stk_menu *stk_menu_create(const char *title,
 			text = dbus_apply_text_attributes(item->text, &attr);
 		}
 
-		if (!text)
+		if (text == NULL)
 			text = strdup(item->text);
 
 		ret->items[i].text = text;
@@ -451,7 +451,7 @@ static void emit_menu_changed(struct ofono_stk *stk)
 
 	signal = dbus_message_new_signal(path, OFONO_STK_INTERFACE,
 						"PropertyChanged");
-	if (!signal) {
+	if (signal == NULL) {
 		ofono_error("Unable to allocate new %s.PropertyChanged signal",
 				OFONO_SIM_APP_INTERFACE);
 
@@ -510,7 +510,7 @@ static DBusMessage *stk_get_properties(DBusConnection *conn,
 	unsigned char icon;
 
 	reply = dbus_message_new_method_return(msg);
-	if (!reply)
+	if (reply == NULL)
 		return NULL;
 
 	dbus_message_iter_init_append(reply, &iter);
@@ -632,13 +632,13 @@ static DBusMessage *stk_register_agent(DBusConnection *conn,
 	stk->default_agent = stk_agent_new(agent_path,
 						dbus_message_get_sender(msg),
 						FALSE);
-	if (!stk->default_agent)
+	if (stk->default_agent == NULL)
 		return __ofono_error_failed(msg);
 
 	stk_agent_set_removed_notify(stk->default_agent,
 					default_agent_notify, stk);
 
-	if (!stk->session_agent)
+	if (stk->session_agent == NULL)
 		stk->current_agent = stk->default_agent;
 
 	return dbus_message_new_method_return(msg);
@@ -656,7 +656,7 @@ static DBusMessage *stk_unregister_agent(DBusConnection *conn,
 					DBUS_TYPE_INVALID) == FALSE)
 		return __ofono_error_invalid_args(msg);
 
-	if (!stk->default_agent)
+	if (stk->default_agent == NULL)
 		return __ofono_error_failed(msg);
 
 	if (!stk_agent_matches(stk->default_agent, agent_path, agent_bus))
@@ -698,7 +698,7 @@ static void menu_selection_envelope_cb(struct ofono_stk *stk, gboolean ok,
 	stk->session_agent = stk_agent_new(agent_path,
 					dbus_message_get_sender(stk->pending),
 					TRUE);
-	if (!stk->session_agent) {
+	if (stk->session_agent == NULL) {
 		reply = __ofono_error_failed(stk->pending);
 
 		goto out;
@@ -729,7 +729,7 @@ static DBusMessage *stk_select_item(DBusConnection *conn,
 	if (stk->pending || stk->session_agent)
 		return __ofono_error_busy(msg);
 
-	if (!menu)
+	if (menu == NULL)
 		return __ofono_error_not_supported(msg);
 
 	if (dbus_message_get_args(msg, NULL,
@@ -838,7 +838,7 @@ static gboolean handle_command_send_sms(const struct stk_command *cmd,
 
 	sms_atom = __ofono_modem_find_atom(modem, OFONO_ATOM_TYPE_SMS);
 
-	if (!sms_atom || !__ofono_atom_get_registered(sms_atom)) {
+	if (sms_atom == NULL || !__ofono_atom_get_registered(sms_atom)) {
 		rsp->result.type = STK_RESULT_TYPE_NOT_CAPABLE;
 		return TRUE;
 	}
@@ -879,7 +879,7 @@ static gboolean handle_command_set_idle_text(const struct stk_command *cmd,
 					cmd->setup_idle_mode_text.text,
 					&cmd->setup_idle_mode_text.text_attr);
 
-		if (!idle_mode_text) {
+		if (idle_mode_text == NULL) {
 			rsp->result.type = STK_RESULT_TYPE_DATA_NOT_UNDERSTOOD;
 			return TRUE;
 		}
@@ -1168,7 +1168,7 @@ static gboolean handle_command_select_item(const struct stk_command *cmd,
 {
 	stk->select_item_menu = stk_menu_create_from_select_item(cmd);
 
-	if (!stk->select_item_menu) {
+	if (stk->select_item_menu == NULL) {
 		rsp->result.type = STK_RESULT_TYPE_DATA_NOT_UNDERSTOOD;
 
 		return TRUE;
@@ -1268,7 +1268,7 @@ static gboolean handle_command_display_text(const struct stk_command *cmd,
 	char *text = dbus_apply_text_attributes(dt->text, &dt->text_attr);
 	int err;
 
-	if (!text) {
+	if (text == NULL) {
 		rsp->result.type = STK_RESULT_TYPE_DATA_NOT_UNDERSTOOD;
 		return TRUE;
 	}
@@ -1430,7 +1430,7 @@ static gboolean handle_command_get_inkey(const struct stk_command *cmd,
 	 */
 	int err;
 
-	if (!text) {
+	if (text == NULL) {
 		rsp->result.type = STK_RESULT_TYPE_DATA_NOT_UNDERSTOOD;
 		return TRUE;
 	}
@@ -1523,7 +1523,7 @@ static gboolean handle_command_get_input(const struct stk_command *cmd,
 	gboolean hidden = (qualifier & (1 << 2)) != 0;
 	int err;
 
-	if (!text) {
+	if (text == NULL) {
 		rsp->result.type = STK_RESULT_TYPE_DATA_NOT_UNDERSTOOD;
 		return TRUE;
 	}
@@ -1567,7 +1567,7 @@ static void call_setup_connected(struct ofono_call *call, void *data)
 	static struct ofono_error error = { .type = OFONO_ERROR_TYPE_FAILURE };
 	static unsigned char facility_rejected_result[] = { 0x9d };
 
-	if (!call || call->status == CALL_STATUS_DISCONNECTED) {
+	if (call == NULL || call->status == CALL_STATUS_DISCONNECTED) {
 		memset(&rsp, 0, sizeof(rsp));
 
 		rsp.result.type = STK_RESULT_TYPE_NETWORK_UNAVAILABLE;
@@ -1593,7 +1593,7 @@ static void call_setup_cancel(struct ofono_stk *stk)
 
 	vc_atom = __ofono_modem_find_atom(__ofono_atom_get_modem(stk->atom),
 						OFONO_ATOM_TYPE_VOICECALL);
-	if (!vc_atom)
+	if (vc_atom == NULL)
 		return;
 
 	vc = __ofono_atom_get_data(vc_atom);
@@ -1641,7 +1641,7 @@ static void confirm_call_cb(enum stk_agent_result result, gboolean confirm,
 	if (vc_atom)
 		vc = __ofono_atom_get_data(vc_atom);
 
-	if (!vc) {
+	if (vc == NULL) {
 		send_simple_response(stk, STK_RESULT_TYPE_NOT_CAPABLE);
 		return;
 	}
@@ -1649,7 +1649,7 @@ static void confirm_call_cb(enum stk_agent_result result, gboolean confirm,
 	if (sc->alpha_id_call_setup) {
 		alpha_id = dbus_apply_text_attributes(sc->alpha_id_call_setup,
 						&sc->text_attr_call_setup);
-		if (!alpha_id) {
+		if (alpha_id == NULL) {
 			send_simple_response(stk,
 					STK_RESULT_TYPE_DATA_NOT_UNDERSTOOD);
 			return;
@@ -1728,7 +1728,7 @@ static gboolean handle_command_set_up_call(const struct stk_command *cmd,
 	if (vc_atom)
 		vc = __ofono_atom_get_data(vc_atom);
 
-	if (!vc) {
+	if (vc == NULL) {
 		rsp->result.type = STK_RESULT_TYPE_NOT_CAPABLE;
 		return TRUE;
 	}
@@ -1743,7 +1743,7 @@ static gboolean handle_command_set_up_call(const struct stk_command *cmd,
 	if (sc->alpha_id_usr_cfm) {
 		alpha_id = dbus_apply_text_attributes(sc->alpha_id_usr_cfm,
 							&sc->text_attr_usr_cfm);
-		if (!alpha_id) {
+		if (alpha_id == NULL) {
 			rsp->result.type = STK_RESULT_TYPE_DATA_NOT_UNDERSTOOD;
 			return TRUE;
 		}
@@ -1776,7 +1776,7 @@ static void send_ussd_cancel(struct ofono_stk *stk)
 
 	atom = __ofono_modem_find_atom(__ofono_atom_get_modem(stk->atom),
 						OFONO_ATOM_TYPE_USSD);
-	if (!atom)
+	if (atom == NULL)
 		return;
 
 	ussd = __ofono_atom_get_data(atom);
@@ -1891,7 +1891,7 @@ static gboolean handle_command_send_ussd(const struct stk_command *cmd,
 	}
 
 	atom = __ofono_modem_find_atom(modem, OFONO_ATOM_TYPE_USSD);
-	if (!atom || !__ofono_atom_get_registered(atom)) {
+	if (atom == NULL || !__ofono_atom_get_registered(atom)) {
 		rsp->result.type = STK_RESULT_TYPE_NOT_CAPABLE;
 		return TRUE;
 	}
@@ -2062,7 +2062,7 @@ static gboolean handle_command_send_dtmf(const struct stk_command *cmd,
 	if (vc_atom)
 		vc = __ofono_atom_get_data(vc_atom);
 
-	if (!vc) {
+	if (vc == NULL) {
 		rsp->result.type = STK_RESULT_TYPE_NOT_CAPABLE;
 		return TRUE;
 	}
@@ -2070,7 +2070,7 @@ static gboolean handle_command_send_dtmf(const struct stk_command *cmd,
 	/* Convert the DTMF string to phone number format */
 	for (pos = 0; cmd->send_dtmf.dtmf[pos] != '\0'; pos++) {
 		digit = strchr(dtmf_from, cmd->send_dtmf.dtmf[pos]);
-		if (!digit) {
+		if (digit == NULL) {
 			rsp->result.type = STK_RESULT_TYPE_DATA_NOT_UNDERSTOOD;
 			return TRUE;
 		}
@@ -2205,7 +2205,7 @@ static gboolean handle_command_play_tone(const struct stk_command *cmd,
 	int err;
 
 	if (pt->tone > sizeof(tone_infos) / sizeof(*tone_infos) ||
-			!tone_infos[pt->tone].name) {
+			tone_infos[pt->tone].name == NULL) {
 		rsp->result.type = STK_RESULT_TYPE_DATA_NOT_UNDERSTOOD;
 
 		return TRUE;
@@ -2213,7 +2213,7 @@ static gboolean handle_command_play_tone(const struct stk_command *cmd,
 
 	text = dbus_apply_text_attributes(pt->alpha_id ? pt->alpha_id : "",
 						&pt->text_attr);
-	if (!text) {
+	if (text == NULL) {
 		rsp->result.type = STK_RESULT_TYPE_DATA_NOT_UNDERSTOOD;
 
 		return TRUE;
@@ -2299,7 +2299,7 @@ void ofono_stk_proactive_command_notify(struct ofono_stk *stk,
 	stk_proactive_command_cancel(stk);
 
 	stk->pending_cmd = stk_command_new_from_pdu(pdu, length);
-	if (!stk->pending_cmd) {
+	if (stk->pending_cmd == NULL) {
 		ofono_error("Can't parse proactive command");
 
 		/*
@@ -2472,7 +2472,7 @@ void ofono_stk_proactive_command_handled_notify(struct ofono_stk *stk,
 
 	cmd = stk_command_new_from_pdu(pdu, length);
 
-	if (!cmd || cmd->status != STK_PARSE_RESULT_OK) {
+	if (cmd == NULL || cmd->status != STK_PARSE_RESULT_OK) {
 		ofono_error("Can't parse proactive command");
 
 		if (cmd)
diff --git a/src/stkagent.c b/src/stkagent.c
index 5cf83e48..83150400 100644
--- a/src/stkagent.c
+++ b/src/stkagent.c
@@ -218,7 +218,7 @@ struct stk_agent *stk_agent_new(const char *path, const char *sender,
 	struct stk_agent *agent = g_try_new0(struct stk_agent, 1);
 	DBusConnection *conn = ofono_dbus_get_connection();
 
-	if (!agent)
+	if (agent == NULL)
 		return NULL;
 
 	agent->path = g_strdup(path);
diff --git a/src/ussd.c b/src/ussd.c
index c4de1770..e0c89cd6 100644
--- a/src/ussd.c
+++ b/src/ussd.c
@@ -76,7 +76,7 @@ struct ssc_entry {
 
 gboolean __ofono_ussd_is_busy(struct ofono_ussd *ussd)
 {
-	if (!ussd)
+	if (ussd == NULL)
 		return FALSE;
 
 	if (ussd->pending || ussd->state != USSD_STATE_IDLE || ussd->req)
@@ -92,7 +92,7 @@ static struct ssc_entry *ssc_entry_create(const char *sc, void *cb, void *data,
 
 	r = g_try_new0(struct ssc_entry, 1);
 
-	if (!r)
+	if (r == NULL)
 		return r;
 
 	r->service = g_strdup(sc);
@@ -125,12 +125,11 @@ gboolean __ofono_ussd_ssc_register(struct ofono_ussd *ussd, const char *sc,
 {
 	struct ssc_entry *entry;
 
-	if (!ussd)
+	if (ussd == NULL)
 		return FALSE;
 
 	entry = ssc_entry_create(sc, cb, data, destroy);
-
-	if (!entry)
+	if (entry == NULL)
 		return FALSE;
 
 	ussd->ss_control_list = g_slist_prepend(ussd->ss_control_list, entry);
@@ -142,13 +141,13 @@ void __ofono_ussd_ssc_unregister(struct ofono_ussd *ussd, const char *sc)
 {
 	GSList *l;
 
-	if (!ussd)
+	if (ussd == NULL)
 		return;
 
 	l = g_slist_find_custom(ussd->ss_control_list, sc,
 				ssc_entry_find_by_service);
 
-	if (!l)
+	if (l == NULL)
 		return;
 
 	ssc_entry_destroy(l->data);
@@ -161,12 +160,11 @@ gboolean __ofono_ussd_passwd_register(struct ofono_ussd *ussd, const char *sc,
 {
 	struct ssc_entry *entry;
 
-	if (!ussd)
+	if (ussd == NULL)
 		return FALSE;
 
 	entry = ssc_entry_create(sc, cb, data, destroy);
-
-	if (!entry)
+	if (entry == NULL)
 		return FALSE;
 
 	ussd->ss_passwd_list = g_slist_prepend(ussd->ss_passwd_list, entry);
@@ -178,13 +176,13 @@ void __ofono_ussd_passwd_unregister(struct ofono_ussd *ussd, const char *sc)
 {
 	GSList *l;
 
-	if (!ussd)
+	if (ussd == NULL)
 		return;
 
 	l = g_slist_find_custom(ussd->ss_passwd_list, sc,
 				ssc_entry_find_by_service);
 
-	if (!l)
+	if (l == NULL)
 		return;
 
 	ssc_entry_destroy(l->data);
@@ -420,7 +418,7 @@ void ofono_ussd_notify(struct ofono_ussd *ussd, int status, int dcs,
 	if (status == OFONO_USSD_STATUS_NOT_SUPPORTED) {
 		ussd_change_state(ussd, USSD_STATE_IDLE);
 
-		if (!ussd->pending)
+		if (ussd->pending == NULL)
 			return;
 
 		reply = __ofono_error_not_supported(ussd->pending);
@@ -430,7 +428,7 @@ void ofono_ussd_notify(struct ofono_ussd *ussd, int status, int dcs,
 	if (status == OFONO_USSD_STATUS_TIMED_OUT) {
 		ussd_change_state(ussd, USSD_STATE_IDLE);
 
-		if (!ussd->pending)
+		if (ussd->pending == NULL)
 			return;
 
 		reply = __ofono_error_timed_out(ussd->pending);
@@ -447,7 +445,7 @@ void ofono_ussd_notify(struct ofono_ussd *ussd, int status, int dcs,
 
 		reply = dbus_message_new_method_return(ussd->pending);
 
-		if (!str)
+		if (str == NULL)
 			str = "";
 
 		dbus_message_iter_init_append(reply, &iter);
@@ -471,7 +469,7 @@ void ofono_ussd_notify(struct ofono_ussd *ussd, int status, int dcs,
 	} else if (ussd->state == USSD_STATE_RESPONSE_SENT) {
 		reply = dbus_message_new_method_return(ussd->pending);
 
-		if (!str)
+		if (str == NULL)
 			str = "";
 
 		dbus_message_append_args(reply, DBUS_TYPE_STRING, &str,
@@ -494,7 +492,7 @@ void ofono_ussd_notify(struct ofono_ussd *ussd, int status, int dcs,
 			signal_name = "NotificationReceived";
 		}
 
-		if (!str)
+		if (str == NULL)
 			str = "";
 
 		g_dbus_emit_signal(conn, path,
@@ -534,7 +532,7 @@ static void ussd_callback(const struct ofono_error *error, void *data)
 		return;
 	}
 
-	if (!ussd->pending)
+	if (ussd->pending == NULL)
 		return;
 
 	reply = __ofono_error_failed(ussd->pending);
@@ -583,7 +581,7 @@ static DBusMessage *ussd_initiate(DBusConnection *conn, DBusMessage *msg,
 	if (!ussd_encode(str, &num_packed, buf))
 		return __ofono_error_invalid_format(msg);
 
-	if (!ussd->driver->request)
+	if (ussd->driver->request == NULL)
 		return __ofono_error_not_implemented(msg);
 
 	DBG("OK, running USSD request");
@@ -609,7 +607,7 @@ static void ussd_response_callback(const struct ofono_error *error, void *data)
 		return;
 	}
 
-	if (!ussd->pending)
+	if (ussd->pending == NULL)
 		return;
 
 	reply = __ofono_error_failed(ussd->pending);
@@ -641,7 +639,7 @@ static DBusMessage *ussd_respond(DBusConnection *conn, DBusMessage *msg,
 	if (!ussd_encode(str, &num_packed, buf))
 		return __ofono_error_invalid_format(msg);
 
-	if (!ussd->driver->request)
+	if (ussd->driver->request == NULL)
 		return __ofono_error_not_implemented(msg);
 
 	ussd->pending = dbus_message_ref(msg);
@@ -696,7 +694,7 @@ static DBusMessage *ussd_cancel(DBusConnection *conn, DBusMessage *msg,
 	if (ussd->cancel)
 		return __ofono_error_busy(msg);
 
-	if (!ussd->driver->cancel)
+	if (ussd->driver->cancel == NULL)
 		return __ofono_error_not_implemented(msg);
 
 	ussd->cancel = dbus_message_ref(msg);
@@ -716,7 +714,7 @@ static DBusMessage *ussd_get_properties(DBusConnection *conn,
 	const char *value;
 
 	reply = dbus_message_new_method_return(msg);
-	if (!reply)
+	if (reply == NULL)
 		return NULL;
 
 	dbus_message_iter_init_append(reply, &iter);
@@ -893,7 +891,7 @@ int __ofono_ussd_initiate(struct ofono_ussd *ussd, int dcs,
 {
 	struct ussd_request *req;
 
-	if (!ussd->driver->request)
+	if (ussd->driver->request == NULL)
 		return -ENOSYS;
 
 	if (__ofono_ussd_is_busy(ussd))
@@ -915,7 +913,7 @@ int __ofono_ussd_initiate(struct ofono_ussd *ussd, int dcs,
 
 void __ofono_ussd_initiate_cancel(struct ofono_ussd *ussd)
 {
-	if (!ussd->req || !ussd->req->cb)
+	if (ussd->req == NULL || ussd->req->cb == NULL)
 		return;
 
 	ussd->req->cb = NULL;
diff --git a/src/voicecall.c b/src/voicecall.c
index a91f14ff..d52428f8 100644
--- a/src/voicecall.c
+++ b/src/voicecall.c
@@ -369,8 +369,7 @@ static DBusMessage *voicecall_get_properties(DBusConnection *conn,
 	DBusMessageIter dict;
 
 	reply = dbus_message_new_method_return(msg);
-
-	if (!reply)
+	if (reply == NULL)
 		return NULL;
 
 	dbus_message_iter_init_append(reply, &iter);
@@ -398,7 +397,7 @@ static DBusMessage *voicecall_deflect(DBusConnection *conn,
 		call->status != CALL_STATUS_WAITING)
 		return __ofono_error_failed(msg);
 
-	if (!vc->driver->deflect)
+	if (vc->driver->deflect == NULL)
 		return __ofono_error_not_implemented(msg);
 
 	if (vc->pending)
@@ -423,10 +422,10 @@ static DBusMessage *voicecall_deflect(DBusConnection *conn,
 static void dial_request_user_cancel(struct ofono_voicecall *vc,
 					struct voicecall *call)
 {
-	if (!vc->dial_req)
+	if (vc->dial_req == NULL)
 		return;
 
-	if (!call || call == vc->dial_req->call)
+	if (call == NULL || call == vc->dial_req->call)
 		dial_request_finish(vc);
 }
 
@@ -533,7 +532,7 @@ static DBusMessage *voicecall_answer(DBusConnection *conn,
 	if (call->status != CALL_STATUS_INCOMING)
 		return __ofono_error_failed(msg);
 
-	if (!vc->driver->answer)
+	if (vc->driver->answer == NULL)
 		return __ofono_error_not_implemented(msg);
 
 	if (vc->pending)
@@ -569,8 +568,7 @@ static struct voicecall *voicecall_create(struct ofono_voicecall *vc,
 	struct voicecall *v;
 
 	v = g_try_new0(struct voicecall, 1);
-
-	if (!v)
+	if (v == NULL)
 		return NULL;
 
 	v->call = call;
@@ -729,7 +727,7 @@ static gboolean voicecall_dbus_register(struct voicecall *v)
 	DBusConnection *conn = ofono_dbus_get_connection();
 	const char *path;
 
-	if (!v)
+	if (v == NULL)
 		return FALSE;
 
 	path = voicecall_build_path(v->vc, v->call);
@@ -879,10 +877,10 @@ static void voicecalls_multiparty_changed(GSList *old, GSList *new)
 		nc = n ? n->data : NULL;
 		oc = o ? o->data : NULL;
 
-		if (oc && (!nc || (nc->call->id > oc->call->id))) {
+		if (oc && (nc == NULL || (nc->call->id > oc->call->id))) {
 			voicecall_emit_multiparty(oc, FALSE);
 			o = o->next;
-		} else if (nc && (!oc || (nc->call->id < oc->call->id))) {
+		} else if (nc && (oc == NULL || (nc->call->id < oc->call->id))) {
 			voicecall_emit_multiparty(nc, TRUE);
 			n = n->next;
 		} else {
@@ -957,7 +955,7 @@ static void voicecalls_release_next(struct ofono_voicecall *vc)
 {
 	struct voicecall *call;
 
-	if (!vc->release_list)
+	if (vc->release_list == NULL)
 		return;
 
 	call = vc->release_list->data;
@@ -997,8 +995,7 @@ static DBusMessage *manager_get_properties(DBusConnection *conn,
 	char **list;
 
 	reply = dbus_message_new_method_return(msg);
-
-	if (!reply)
+	if (reply == NULL)
 		return NULL;
 
 	dbus_message_iter_init_append(reply, &iter);
@@ -1046,8 +1043,7 @@ static struct ofono_call *synthesize_outgoing_call(struct ofono_voicecall *vc,
 	struct ofono_call *call;
 
 	call = g_try_new0(struct ofono_call, 1);
-
-	if (!call)
+	if (call == NULL)
 		return call;
 
 	call->id = __ofono_modem_callid_next(modem);
@@ -1102,11 +1098,11 @@ static struct voicecall *dial_handle_result(struct ofono_voicecall *vc,
 	}
 
 	call = synthesize_outgoing_call(vc, number);
-	if (!call)
+	if (call == NULL)
 		return NULL;
 
 	v = voicecall_create(vc, call);
-	if (!v)
+	if (v == NULL)
 		return NULL;
 
 	v->detect_time = time(NULL);
@@ -1178,7 +1174,7 @@ static DBusMessage *manager_dial(DBusConnection *conn,
 	if (clir_string_to_clir(clirstr, &clir) == FALSE)
 		return __ofono_error_invalid_format(msg);
 
-	if (!vc->driver->dial)
+	if (vc->driver->dial == NULL)
 		return __ofono_error_not_implemented(msg);
 
 	if (voicecalls_have_incoming(vc))
@@ -1225,7 +1221,7 @@ static DBusMessage *manager_transfer(DBusConnection *conn,
 	if ((numactive != 1) && (numheld != 1))
 		return __ofono_error_failed(msg);
 
-	if (!vc->driver->transfer)
+	if (vc->driver->transfer == NULL)
 		return __ofono_error_not_implemented(msg);
 
 	vc->pending = dbus_message_ref(msg);
@@ -1265,7 +1261,7 @@ static DBusMessage *manager_swap_calls(DBusConnection *conn,
 	if (voicecalls_have_waiting(vc))
 		return __ofono_error_failed(msg);
 
-	if (!vc->driver->hold_all_active)
+	if (vc->driver->hold_all_active == NULL)
 		return __ofono_error_not_implemented(msg);
 
 	vc->pending = dbus_message_ref(msg);
@@ -1286,7 +1282,7 @@ static DBusMessage *manager_release_and_answer(DBusConnection *conn,
 	if (!voicecalls_have_waiting(vc))
 		return __ofono_error_failed(msg);
 
-	if (!vc->driver->release_all_active)
+	if (vc->driver->release_all_active == NULL)
 		return __ofono_error_not_implemented(msg);
 
 	vc->pending = dbus_message_ref(msg);
@@ -1314,7 +1310,7 @@ static DBusMessage *manager_hold_and_answer(DBusConnection *conn,
 	if (voicecalls_have_active(vc) && voicecalls_have_held(vc))
 		return __ofono_error_failed(msg);
 
-	if (!vc->driver->hold_all_active)
+	if (vc->driver->hold_all_active == NULL)
 		return __ofono_error_not_implemented(msg);
 
 	vc->pending = dbus_message_ref(msg);
@@ -1448,7 +1444,7 @@ static DBusMessage *multiparty_private_chat(DBusConnection *conn,
 
 	c = strrchr(callpath, '/');
 
-	if (!c || strncmp(path, callpath, c-callpath))
+	if (c == NULL || strncmp(path, callpath, c-callpath))
 		return __ofono_error_not_found(msg);
 
 	if (!sscanf(c, "/voicecall%2u", &id))
@@ -1460,7 +1456,7 @@ static DBusMessage *multiparty_private_chat(DBusConnection *conn,
 			break;
 	}
 
-	if (!l)
+	if (l == NULL)
 		return __ofono_error_not_found(msg);
 
 	/*
@@ -1471,7 +1467,7 @@ static DBusMessage *multiparty_private_chat(DBusConnection *conn,
 	if (voicecalls_have_held(vc))
 		return __ofono_error_failed(msg);
 
-	if (!vc->driver->private_chat)
+	if (vc->driver->private_chat == NULL)
 		return __ofono_error_not_implemented(msg);
 
 	vc->pending = dbus_message_ref(msg);
@@ -1540,7 +1536,7 @@ static DBusMessage *multiparty_create(DBusConnection *conn,
 	if (!voicecalls_have_held(vc) || !voicecalls_have_active(vc))
 		return __ofono_error_failed(msg);
 
-	if (!vc->driver->create_multiparty)
+	if (vc->driver->create_multiparty == NULL)
 		return __ofono_error_not_implemented(msg);
 
 	vc->pending = dbus_message_ref(msg);
@@ -1558,13 +1554,13 @@ static DBusMessage *multiparty_hangup(DBusConnection *conn,
 	if (vc->pending)
 		return __ofono_error_busy(msg);
 
-	if (!vc->driver->release_specific)
+	if (vc->driver->release_specific == NULL)
 		return __ofono_error_not_implemented(msg);
 
-	if (!vc->driver->release_all_held)
+	if (vc->driver->release_all_held == NULL)
 		return __ofono_error_not_implemented(msg);
 
-	if (!vc->driver->release_all_active)
+	if (vc->driver->release_all_active == NULL)
 		return __ofono_error_not_implemented(msg);
 
 	if (vc->multiparty_list == NULL) {
@@ -1628,7 +1624,7 @@ static DBusMessage *manager_tone(DBusConnection *conn,
 	if (vc->pending)
 		return __ofono_error_busy(msg);
 
-	if (!vc->driver->send_tones)
+	if (vc->driver->send_tones == NULL)
 		return __ofono_error_not_implemented(msg);
 
 	/* Send DTMFs only if we have at least one connected call */
@@ -1760,7 +1756,7 @@ void ofono_voicecall_disconnected(struct ofono_voicecall *vc, int id,
 	l = g_slist_find_custom(vc->call_list, GUINT_TO_POINTER(id),
 				call_compare_by_id);
 
-	if (!l) {
+	if (l == NULL) {
 		ofono_error("Plugin notified us of call disconnect for"
 				" unknown call");
 		return;
@@ -1838,15 +1834,13 @@ void ofono_voicecall_notify(struct ofono_voicecall *vc,
 	__ofono_modem_callid_hold(modem, call->id);
 
 	newcall = g_memdup(call, sizeof(struct ofono_call));
-
-	if (!newcall) {
+	if (newcall == NULL) {
 		ofono_error("Unable to allocate call");
 		goto error;
 	}
 
 	v = voicecall_create(vc, newcall);
-
-	if (!v) {
+	if (v == NULL) {
 		ofono_error("Unable to allocate voicecall_data");
 		goto error;
 	}
@@ -2363,7 +2357,7 @@ int __ofono_voicecall_dial(struct ofono_voicecall *vc,
 	if (!valid_phone_number_format(addr))
 		return -EINVAL;
 
-	if (!vc->driver->dial)
+	if (vc->driver->dial == NULL)
 		return -ENOSYS;
 
 	if (interaction == OFONO_VOICECALL_INTERACTION_DISCONNECT &&
@@ -2419,7 +2413,7 @@ int __ofono_voicecall_dial(struct ofono_voicecall *vc,
 
 void __ofono_voicecall_dial_cancel(struct ofono_voicecall *vc)
 {
-	if (!vc->dial_req || !vc->dial_req->cb)
+	if (vc->dial_req == NULL || vc->dial_req->cb == NULL)
 		return;
 
 	vc->dial_req->cb = NULL;
@@ -2431,7 +2425,7 @@ static void tone_request_cb(const struct ofono_error *error, void *data)
 	struct tone_queue_entry *entry = g_queue_peek_head(vc->toneq);
 	int len = 0;
 
-	if (!entry)
+	if (entry == NULL)
 		return;
 
 	/*
@@ -2477,7 +2471,7 @@ static gboolean tone_request_run(gpointer user_data)
 
 	vc->tone_source = 0;
 
-	if (!entry)
+	if (entry == NULL)
 		return FALSE;
 
 	len = strcspn(entry->left, "pP");
@@ -2504,7 +2498,7 @@ int __ofono_voicecall_tone_send(struct ofono_voicecall *vc,
 				const char *tone_str,
 				ofono_voicecall_tone_cb_t cb, void *user_data)
 {
-	if (!vc->driver->send_tones)
+	if (vc->driver->send_tones == NULL)
 		return -ENOSYS;
 
 	/* Send DTMFs only if we have at least one connected call */