@Override
    @SuppressWarnings("CloneDoesntCallSuperClone,CloneDoesntDeclareCloneNotSupportedException")
    public MapReduce<MK, MV, RK, RV, R> clone() {
        return this;
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/computer/util/StaticMapReduce.java