[FIX] email_template: ensure non-empty context when rendering template'

bzr revid: odo@openerp.com-20120322141153-8u3kia3k125et6b5

addons/email_template/email_template.py

@@ -57,6 +57,8 @@ class email_template(osv.osv):
            :param int res_id: id of the document record this mail is related to.
         """
         if not template: return u""
+        if context is None:
+            context = {}
         try:
             template = tools.ustr(template)
             record = None