private static PsiElement checkSanity(PsiElement element, PsiElement sibling) {
      if (sibling == PsiUtilCore.NULL_PSI_ELEMENT) throw new PsiInvalidElementAccessException(element, "Sibling of "+element+" is NULL_PSI_ELEMENT");
      return sibling;
    }
private static PsiElement checkSanity(PsiElement element, PsiElement sibling)