@Override
    public void merge(final Traverser.Admin<?> other) {
        if (!other.getTags().isEmpty()) {
            if (this.tags == null) this.tags = new HashSet<>();
            this.tags.addAll(other.getTags());
        }
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/traverser/O_Traverser.java