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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 get_user_vault_instance_or_none(self, user):
 """Returns a vault_id string or None"""

        qset = self.filter(user=user)
        if not qset:
            return None
        
        if qset.count() > 1:
            raise Exception('This app does not currently support multiple vault ids')
        
        return qset.get()