String calcPlaceholderText() {
    PsiElement psiElement = myElement.getPsi();
    if (psiElement == null) return null;
    FoldingBuilder foldingBuilder = LanguageFolding.INSTANCE.forLanguage(psiElement.getLanguage());
    if (foldingBuilder == null) return null;
    return foldingBuilder instanceof FoldingBuilderEx
           ? ((FoldingBuilderEx)foldingBuilder).getPlaceholderText(myElement, myRange)
           : foldingBuilder.getPlaceholderText(myElement);
  }
String calcPlaceholderText()