@Override
        public Traversal<Edge, ? extends Property<Object>> get_g_E_properties_hasKeyXnullX() {
            return g.E().properties().hasKey(null);
        }
@author Marko A. Rodriguez (http://markorodriguez.com)
@author Stephen Mallette (http://stephen.genoprime.com)
gremlin-test/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/filter/HasTest.java