@Override
    public FluentFuture<V> withExecutor(Executor executor) {
      if (this.executor == executor) {
        return this;
      }
      return new WrapingFluentFuture<>(delegate(), executor);
    }
Provides default wrapping implementation of {@link FluentFuture}
mongo/src/org/immutables/mongo/concurrent/FluentFutures.java