private static @Nullable TokenInfo merge(TokenInfo t1, TokenInfo t2) {
    if (t1 instanceof WSTokenInfo && t2 instanceof WSTokenInfo) return t1;
    if (t1 instanceof PsiToken && t2 instanceof PsiToken) return mergePsiTokens((PsiToken)t1, (PsiToken)t2);
    return null;
  }
private static @Nullable TokenInfo merge(TokenInfo t1, TokenInfo t2)