@Override
    public void add(final String key, final Object value) {
        this.mainMemory.checkKeyValue(key, value);
        final Object v = this.workerMemory.get(key);
        this.workerMemory.put(key, null == v ? value : this.reducers.get(key).apply(v, value));
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
tinkergraph-gremlin/src/main/java/org/apache/tinkerpop/gremlin/tinkergraph/process/computer/TinkerWorkerMemory.java