@Override
    protected List<Traversal> getTraversals() {
        return Arrays.asList(
                __.optional(out()),
                __.optional(out("knows")),
                __.optional(in().out()),
                __.optional(out("created")),
                __.optional(in().in()),
                __.optional(identity())
        );
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
gremlin-core/src/test/java/org/apache/tinkerpop/gremlin/process/traversal/step/branch/OptionalStepTest.java