The filename of the attachment

        :param file_name: The filename of the attachment
        :type file_name: FileName, string

def file_name(self, value):
        """The filename of the attachment

        :param file_name: The filename of the attachment
        :type file_name: FileName, string
        """
        if isinstance(value, FileName):
            self._file_name = value
        else:
            self._file_name = FileName(value)