@Override
    public void dropKeyIndex(final String key) {
        if (this.index.containsKey(key))
            this.index.remove(key).clear();

        this.indexedKeys.remove(key);
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
tinkergraph-gremlin/src/main/java/org/apache/tinkerpop/gremlin/tinkergraph/structure/TinkerIndex.java