code: def _multi_value_field(self, field):
          
          for field_dict in self.schema:
              if field_dict['field_name'] == field:
                  return field_dict['multi_valued'] == 'true'
          return False
docs: Private method that returns `True` if a field is multi-valued, else
          `False`.
  
          Required arguemnts:
              `field` -- The field to lookup
  
          Returns a boolean value indicating whether the field is multi-valued.