code: static TypeMirror getCreatorArg(Elements elements, Types types, DeclaredType creatorType) {
      TypeElement creatorElement = elements.getTypeElement(PARCELABLE_CREATOR_CLASS_NAME);
      TypeParameterElement param = creatorElement.getTypeParameters().get(0);
      return paramAsMemberOf(types, creatorType, param);
    }
docs: Returns the {@link TypeMirror} argument found in a given {@code Parcelable.Creator} type.