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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 list_files(self, node=None):
 """ Returns the Model files. :param node: Node to start walking from. :type node: AbstractNode or AbstractCompositeNode or Object :return: FileNode nodes. :rtype: list """


        return [file_node.path for file_node in self.list_file_nodes(node) if file_node.path]