*
   * TODO: cpovirk - Is this an issue anywhere anymore? It looks to have been fixed for Java 8
   * (https://bugs.openjdk.org/browse/JDK-7121314) and before Lollipop
   * (https://r.android.com/47508). We *would* need to worry for J2KT, whose own concurrency support
   * is evolving (b/381065164, b/458160722), but this class is @J2ktIncompatible.
   *
   * 2. The superclass toArray() method declares the more general return type `@Nullable Object[]`,

   */
  public static <E> ImmutableSet<E> of(E e1) {
    return new SingletonImmutableSet<>(e1);
  }

  /*
   * TODO: b/315526394 - Skip the Builder entirely for the of(...) methods, since we don't need to
   * worry that we might trigger the fallback to the JDK-backed implementation? (The varargs one
   * _could_, so we could keep it as it is. Or we could convince ourselves that hash flooding is
   * unlikely in practice there, too.)
   */