@Override
  @ParametricNullness
  public E removeLast() {
    return delegate().removeLast();
  }

  @CanIgnoreReturnValue
  @Override
  public boolean removeFirstOccurrence(@Nullable Object o) {
    return delegate().removeFirstOccurrence(o);
  }

  @CanIgnoreReturnValue
  @Override
  public boolean removeLastOccurrence(@Nullable Object o) {
    return delegate().removeLastOccurrence(o);
  }

    public @Nullable E peekLast() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.peekLast();
    }

    @Override
    public boolean removeFirstOccurrence(Object o) {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.removeFirstOccurrence(o);
    }

    @Override
    public boolean removeLastOccurrence(Object o) {
      assertTrue(Thread.holdsLock(mutex));

    public @Nullable E peekLast() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.peekLast();
    }

    @Override
    public boolean removeFirstOccurrence(Object o) {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.removeFirstOccurrence(o);
    }

    @Override
    public boolean removeLastOccurrence(Object o) {
      assertTrue(Thread.holdsLock(mutex));

      synchronized (mutex) {
        return delegate().peekLast();
      }
    }

    @Override
    public boolean removeFirstOccurrence(@Nullable Object o) {
      synchronized (mutex) {
        return delegate().removeFirstOccurrence(o);
      }
    }

    @Override
    public boolean removeLastOccurrence(@Nullable Object o) {
      synchronized (mutex) {

      synchronized (mutex) {
        return delegate().peekLast();
      }
    }

    @Override
    public boolean removeFirstOccurrence(@Nullable Object o) {
      synchronized (mutex) {
        return delegate().removeFirstOccurrence(o);
      }
    }

    @Override
    public boolean removeLastOccurrence(@Nullable Object o) {
      synchronized (mutex) {