code: def valueFromString(self, value, context=None):
          
          model = self.referenceModel()
          return model(value, context=context)
docs: Re-implements the orb.Column.valueFromString method to
          lookup a reference object based on the given value.
  
          :param value: <str>
          :param context: <orb.Context> || None
  
          :return: <orb.Model> || None