Return a json dictionary representing this model.

def _to_dict(self):
        """Return a json dictionary representing this model."""
        _dict = {}
        if hasattr(self, 'dialog_node') and self.dialog_node is not None:
            _dict['dialog_node'] = self.dialog_node
        if hasattr(self, 'title') and self.title is not None:
            _dict['title'] = self.title
        if hasattr(self, 'conditions') and self.conditions is not None:
            _dict['conditions'] = self.conditions
        return _dict