* use the {@code HashMap} constructor directly, taking advantage of <a
   * 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

   * use the {@code HashMap} constructor directly, taking advantage of <a
   * 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