* href="http://goo.gl/iz2Wi">"diamond" syntax</a>.
   *
   * @return a new, empty {@code HashMap}
   */
  public static <K extends @Nullable Object, V extends @Nullable Object>
      HashMap<K, V> newHashMap() {
    return new HashMap<>();
  }

  /**
   * Creates a <i>mutable</i> {@code HashMap} instance with the same mappings as the specified map.
   *