code: public static TypeMirror getApplicationSupertype(TypeElement type) {
      TypeMirror supertype = type.getSuperclass();
      return Keys.isPlatformType(supertype.toString()) ? null : supertype;
    }
docs: Returns the supertype, or {@code null} if the supertype is a platform
  class. This is intended for annotation processors that assume platform
  classes will never be annotated with application annotations.