@Override
    public Set<String> keys() {
        if (null == this.properties) return Collections.emptySet();
        return TinkerHelper.inComputerMode((AbstractTinkerGraph) graph()) ?
                Vertex.super.keys() :
                this.properties.keySet();
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
tinkergraph-gremlin/src/main/java/org/apache/tinkerpop/gremlin/tinkergraph/structure/TinkerVertex.java