* href="https://docs.oracle.com/javase/tutorial/java/generics/genTypeInference.html#type-inference-instantiation">"diamond"
   * syntax</a>.
   *
   * @return a new, empty {@code HashMap}
   */
  @SuppressWarnings("NonApiType") // acts as a direct substitute for a constructor call
  public static <K extends @Nullable Object, V extends @Nullable Object>
      HashMap<K, V> newHashMap() {
    return new HashMap<>();
  }

  /**