code: def to_dict(self):
          
          return {
              "type": self.type,
              "name": self.name,
              "group_by_key": self.group_by_key,
              "role": self.role,
              "units": self.units,
              "options": self.build_options()
          }
docs: Converts the column to a dictionary representation accepted
          by the Citrination server.
  
          :return: Dictionary with basic options, plus any column type specific
              options held under the "options" key
          :rtype: dict