def do_execute(self):
        """
        The actual execution of the actor.

        :return: None if successful, otherwise error message
        :rtype: str
        """
        formatstr = str(self.resolve_option("format"))
        expanded = self.storagehandler.expand(formatstr)
        self._output.append(Token(expanded))
        return None
The actual execution of the actor.

        :return: None if successful, otherwise error message
        :rtype: str