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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def assistant_fallback_actions(self):
 """ Access the assistant_fallback_actions :returns: twilio.rest.preview.understand.assistant.assistant_fallback_actions.AssistantFallbackActionsList :rtype: twilio.rest.preview.understand.assistant.assistant_fallback_actions.AssistantFallbackActionsList """

        if self._assistant_fallback_actions is None:
            self._assistant_fallback_actions = AssistantFallbackActionsList(
                self._version,
                assistant_sid=self._solution['sid'],
            )
        return self._assistant_fallback_actions