Assert fields in exclude are model fields

Author: maryokhin

rest_framework/serializers.py

@@ -880,6 +880,10 @@ def get_fields(self):
             exclude = getattr(self.Meta, 'exclude', None)
             if exclude is not None:
                 for field_name in exclude:
+                    assert field_name in fields, (
+                        'The field in the `exclude` option must be a model field. Got %s.' %
+                        field_name
+                    )
                     fields.remove(field_name)
 
         # Determine the set of model fields, and the fields that they map to.