@Nullable
  public static String charLiteralString(PsiLiteralExpression expression) {
    final Object value = expression.getValue();
    if (!(value instanceof String) || ((CharSequence)value).length() > 1) {
      throw new IllegalArgumentException();
    }
    final String content = expression.isTextBlock()
                           ? getTextBlockText(expression)
                           : getStringLiteralContent(expression);
    if (content == null) {
      return null;
    }
    switch (content) {
      case "'": return "'\\''";
      case "\\\"": return "'\"'";
      default: return '\'' + content + '\'';
    }
  }
@Nullable
  public static String charLiteralString(PsiLiteralExpression expression)