code: def __parameter_enum(self, final_subfield):
      
      if isinstance(final_subfield, messages.EnumField):
        enum_descriptor = {}
        for enum_value in final_subfield.type.to_dict().keys():
          enum_descriptor[enum_value] = {'backendValue': enum_value}
        return enum_descriptor
docs: Returns enum descriptor of final subfield if it is an enum.
  
      An enum descriptor is a dictionary with keys as the names from the enum and
      each value is a dictionary with a single key "backendValue" and value equal
      to the same enum name used to stored it in the descriptor.
  
      The key "description" can also be used next to "backendValue", but protorpc
      Enum classes have no way of supporting a description for each value.
  
      Args:
        final_subfield: A simple field from the end of a subfield list.
  
      Returns:
        The enum descriptor for the field, if it's an enum descriptor, else
            returns None.