private static boolean isSubclass(@Nullable PsiClass childClass,
                                      @Nullable PsiClass parent) {
      if (childClass == null) {
        return false;
      }
      if (parent == null) {
        return false;
      }
      return childClass.isInheritor(parent, true);
    }
private static boolean isSubclass(@Nullable PsiClass childClass,
                                      @Nullable PsiClass parent)