code: protected int standardHashCode() {
      K k = getKey();
      V v = getValue();
      return ((k == null) ? 0 : k.hashCode()) ^ ((v == null) ? 0 : v.hashCode());
    }
docs: A sensible definition of {@link #hashCode()} in terms of {@link #getKey()} and {@link
  #getValue()}. If you override either of these methods, you may wish to override {@link
  #hashCode()} to forward to this implementation.
  
  @since 7.0