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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 _end_session(self, kill=None):
 """End the client session."""

        if self._stc:
            if kill is None:
                kill = os.environ.get('STC_SESSION_TERMINATE_ON_DISCONNECT')
                kill = _is_true(kill)
            self._stc.end_session(kill)
            self._stc = None