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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 _try_next(self, get_more_allowed):
 """Advance the cursor blocking for at most one getMore command."""

        if not len(self.__data) and not self.__killed and get_more_allowed:
            self._refresh()
        if len(self.__data):
            coll = self.__collection
            return coll.database._fix_outgoing(self.__data.popleft(), coll)
        else:
            return None