public void setDedupLabels(final Set<String> labels) {
        if (!labels.isEmpty()) {
            this.dedups = new HashSet<>();
            this.dedupLabels = new HashSet<>(labels);
            if (null != this.keepLabels)
                this.keepLabels.addAll(this.dedupLabels);
        }
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/MatchStep.java