* use the {@code EnumMap} constructor directly, taking advantage of <a
   * href="http://goo.gl/iz2Wi">"diamond" syntax</a>.
   *
   * @param map the map from which to initialize this {@code EnumMap}
   * @return a new {@code EnumMap} initialized with the mappings from {@code map}
   * @throws IllegalArgumentException if {@code m} is not an {@code EnumMap} instance and contains
   *     no mappings
   */