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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 Instance(reactor=None):
 """ Get the local node instance. Args: reactor: (optional) custom reactor to use in NodeLeader. Returns: NodeLeader: instance. """

        if NodeLeader._LEAD is None:
            NodeLeader._LEAD = NodeLeader(reactor)
        return NodeLeader._LEAD