Return a json dictionary representing this model.

def _to_dict(self):
        """Return a json dictionary representing this model."""
        _dict = {}
        if hasattr(self, 'party') and self.party is not None:
            _dict['party'] = self.party
        if hasattr(self, 'importance') and self.importance is not None:
            _dict['importance'] = self.importance
        if hasattr(self, 'role') and self.role is not None:
            _dict['role'] = self.role
        if hasattr(self, 'addresses') and self.addresses is not None:
            _dict['addresses'] = [x._to_dict() for x in self.addresses]
        if hasattr(self, 'contacts') and self.contacts is not None:
            _dict['contacts'] = [x._to_dict() for x in self.contacts]
        return _dict