def close(self):
        """called before visiting project (i.e set of modules)"""
        if self.linter.is_message_enabled("cyclic-import"):
            graph = self._import_graph_without_ignored_edges()
            vertices = list(graph)
            for cycle in get_cycles(graph, vertices=vertices):
                self.add_message("cyclic-import", args=" -> ".join(cycle))
called before visiting project (i.e set of modules)