}

  @Override
  public void execute(Runnable command) {
    Preconditions.checkNotNull(command, "command must not be null!");
    delegate.execute(command);
  }

  @Override
  public ListenableScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit) {
    Preconditions.checkNotNull(command, "command must not be null");
    Preconditions.checkNotNull(unit, "unit must not be null!");

  }

  @Override
  public void execute(Runnable command) {
    Preconditions.checkNotNull(command, "command must not be null!");
    delegate.execute(command);
  }

  @Override
  public ListenableScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit) {
    Preconditions.checkNotNull(command, "command must not be null");
    Preconditions.checkNotNull(unit, "unit must not be null!");