@Override
    public NavigableSet<K> navigableKeySet() {
      return fromMap().navigableKeySet();
    }

    @Override
    @CheckForNull
    public Entry<K, V2> pollFirstEntry() {
      return transformEntry(fromMap().pollFirstEntry());
    }

    @Override
    @CheckForNull
    public Entry<K, V2> pollLastEntry() {
      return transformEntry(fromMap().pollLastEntry());
    }

        }
        return navigableKeySet;
      }
    }

    @Override
    @CheckForNull
    public Map.Entry<K, V> pollFirstEntry() {
      synchronized (mutex) {
        return nullableSynchronizedEntry(delegate().pollFirstEntry(), mutex);
      }
    }

    @Override
    @CheckForNull
    public Map.Entry<K, V> pollLastEntry() {
      synchronized (mutex) {

        }
        return navigableKeySet;
      }
    }

    @Override
    @CheckForNull
    public Map.Entry<K, V> pollFirstEntry() {
      synchronized (mutex) {
        return nullableSynchronizedEntry(delegate().pollFirstEntry(), mutex);
      }
    }

    @Override
    @CheckForNull
    public Map.Entry<K, V> pollLastEntry() {
      synchronized (mutex) {

   * @deprecated Unsupported operation.
   */
  @CanIgnoreReturnValue
  @Deprecated
  @Override
  @DoNotCall("Always throws UnsupportedOperationException")
  @CheckForNull
  public final Entry<E> pollFirstEntry() {
    throw new UnsupportedOperationException();
  }

  /**
   * {@inheritDoc}
   *
   * <p>This implementation is guaranteed to throw an {@link UnsupportedOperationException}.
   *

   * @deprecated Unsupported operation.
   */
  @CanIgnoreReturnValue
  @Deprecated
  @Override
  @DoNotCall("Always throws UnsupportedOperationException")
  @CheckForNull
  public final Entry<K, V> pollFirstEntry() {
    throw new UnsupportedOperationException();
  }

  /**
   * Guaranteed to throw an exception and leave the map unmodified.
   *
   * @throws UnsupportedOperationException always

   * @deprecated Unsupported operation.
   */
  @CanIgnoreReturnValue
  @Deprecated
  @Override
  @DoNotCall("Always throws UnsupportedOperationException")
  @CheckForNull
  public final Entry<K, V> pollFirstEntry() {
    throw new UnsupportedOperationException();
  }

  /**
   * Guaranteed to throw an exception and leave the map unmodified.
   *
   * @throws UnsupportedOperationException always