Avoid "patching" the registry, as this introduces inconsistencies (some field
attributes are lost). Instead, proceed as follows:
- update the definition of custom fields in database;
- clear the corresponding cache on the registry (this was missing);
- setup the models in registry (this reloads the custom models and fields);
- update the database schema of the models based on the registry.
This makes the update of custom fields simpler and more robust.
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