code: def get_fields(self):
          
          fields = super(GeoModelSerializer, self).get_fields()
          # Set the geometry field name when it's undeclared.
          if not self.Meta.geom_field:
              for name, field in fields.items():
                  if isinstance(field, GeometryField):
                      self.Meta.geom_field = name
                      break
          return fields
docs: Returns a fields dict for this serializer with a 'geometry' field
          added.