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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 state(self, states=None):
 """Filter by state. :param tags: States to filter. :type tags: ``list`` :return: A list of Node objects. :rtype: ``list`` of :class:`Node` """

        if states is None or not states:
            return self
        nodes = []
        for node in self.nodes:
            if any(state.lower() == node.state.lower() for state in states):
                nodes.append(node)
        self.nodes = nodes
        return self