Error in dynamic_graph.collapse_namespaces

When converting a tensorflow model to a uff model, the dynamic_graph.collapse_namespaces(namespace_plugin_map, exclude_nodes=nodes) will cause an error: None is not iterable. I solve this by modifying the code as below.
In the file: /usr/local/lib/python3.5/dist-packages/graphsurgeon/

def get_plugin_node(node_name):
            # Get the default plugin node provided by the user, or return None if this
            # does not belong in a plugin.
            if node_name in exclude_node_names:
                # Don't put this node into a plugin, treat as normal node instead.
                return None, None