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

def __set_text_field(text, text_type):
    # type: (str, str) -> Union[None, PlainText, RichText]
    """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
    """
    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