@Override
    public Vertex addVertex(final Object... keyValues) {
        throw Exceptions.vertexAdditionsNotSupported();
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
@author Stephen Mallette (http://stephen.genoprime.com)
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/util/empty/EmptyGraph.java