              field_kwargs.pop('allow_blank', None)
  
          if postgres_fields and isinstance(model_field, postgres_fields.JSONField):
              # Populate the `encoder` argument of `JSONField` instances generated
              # for the PostgreSQL specific `JSONField`.
              field_kwargs['encoder'] = getattr(model_field, 'encoder', None)
  
          if postgres_fields and isinstance(model_field, postgres_fields.ArrayField):
              # Populate the `child` argument on `ListField` instances generated
              # for the PostgreSQL specific `ArrayField`.
 
</s> remove         if postgres_fields and isinstance(model_field, postgres_fields.JSONField):
 </s> add         is_django_jsonfield = hasattr(models, 'JSONField') and isinstance(model_field, models.JSONField)
        if (postgres_fields and isinstance(model_field, postgres_fields.JSONField)) or is_django_jsonfield: </s> remove             (postgres_fields and isinstance(model_field, postgres_fields.JSONField)):
 </s> add             (postgres_fields and isinstance(model_field, postgres_fields.JSONField)) or \
            (hasattr(models, 'JSONField') and isinstance(model_field, models.JSONField)):
            # for the model `JSONField`.
              field_kwargs.pop('allow_blank', None)
  
          if postgres_fields and isinstance(model_field, postgres_fields.JSONField):
              # Populate the `encoder` argument of `JSONField` instances generated
            # for the model `JSONField`.
              field_kwargs['encoder'] = getattr(model_field, 'encoder', None)
  
          if postgres_fields and isinstance(model_field, postgres_fields.ArrayField):
              # Populate the `child` argument on `ListField` instances generated
              # for the PostgreSQL specific `ArrayField`.
keep keep keep keep replace keep keep keep keep keep
 Add support for Django 3.1 JSONField (#7467)

Django 3.1 adds a new generic JSONField to replace the PostgreSQL-specific one. This adds support for the new field type, which should behave the same as the existing PostgreSQL field.

Django's new JSONField also includes support for a custom "decoder", so add support for that in the serializer field. 
rest_framework/serializers.py