return get(key) != null;
  }

  @Override
  public boolean containsValue(@CheckForNull Object value) {
    return values().contains(value);
  }

  // Overriding to mark it Nullable
  @Override
  @CheckForNull
  public abstract V get(@CheckForNull Object key);

  /**
   * {@inheritDoc}
   *
   * <p>See <a