* Make `RegistrationSerializer` and `EmailSerializerBase` fields a tuple.
Notes
`RegistrationSerializer` or `EmailSerializerBase` subclasses adding new fields
with a `list` will generate a `TypeError`:
class CustomRegistration(RegistrationSerializer):
class Meta(RegistrationSerializer.Meta):
fields = RegistrationSerializer.Meta.fields + ['custom_field']
TypeError: can only concatenate tuple (not "list") to tuple`
To fix the previous error we use a tuple instead:
class CustomRegistration(RegistrationSerializer):
class Meta(RegistrationSerializer.Meta):
fields = RegistrationSerializer.Meta.fields + ('custom_field',)