protected Graph getGraph() {
        return this.getTraversal().getGraph().get();
    }
This implementation should only be used as a mechanism for supporting {@link PartitionStrategy}. Using this
with {@link GraphTraversal#with(String,Object)} will have an ill effect of simply acting like a call to
{@link GraphTraversal#property(Object, Object, Object...)}. No mutating steps currently support use of
{@link GraphTraversal#with(String,Object)} so perhaps it's best to not start with that now.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/MergeElementStep.java