code: def __set_text_field(text, text_type):
      # type: (str, str) -> Union[None, PlainText, RichText]
      
      if text:
          if text_type not in [PLAIN_TEXT_TYPE, RICH_TEXT_TYPE]:
              raise ValueError("Invalid type provided: {}".format(text_type))
  
          if text_type == PLAIN_TEXT_TYPE:
              return PlainText(text=text)
          else:
              return RichText(text=text)
      else:
          return None
docs: Helper method to create text field according to text type.
  
      :type text: str
      :param text_type: Type of the primary text field. Allowed values
          are `PlainText` and `RichText`.
      :type text_type: str
      :return: Object of type
          :py:class:`ask_sdk_model.interfaces.display.PlainText` or
          :py:class:`ask_sdk_model.interfaces.display.RichText` depending
          on text_type
      :rtype: object
      :raises: ValueError