static Optionalish createIfOptional(TypeMirror type) {
    if (isOptional(type)) {
      return new Optionalish(MoreTypes.asDeclared(type));
    } else {
      return null;
    }
  }
Returns an instance wrapping the given TypeMirror, or null if it is not any kind of Optional.

@param type the TypeMirror for the original optional type, for example {@code
    Optional<String>}.
value/src/main/java/com/google/auto/value/processor/Optionalish.java