@Override
    public void replaceLocalChild(final Traversal.Admin<?, ?> oldTraversal, final Traversal.Admin<?, ?> newTraversal) {
        if (null != this.keyTraversal && this.keyTraversal.equals(oldTraversal))
            this.keyTraversal = this.integrateChild(newTraversal);
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/GroupCountStep.java