@Override
    public int hashCode() {
        int result = super.hashCode();
        for (final String propertyKey : this.propertyKeys) {
            result ^= Objects.hashCode(propertyKey);
        }
        return result;
    }
Converts a {@link Element} to a {@code Map}.

@author Marko A. Rodriguez (http://markorodriguez.com)
@author Daniel Kuppitz (http://gremlin.guru)
@author Stephen Mallette (http://stephen.genoprime.com)
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/ElementMapStep.java