@Nullable
    private static PsiExpression extractDelimiter(PsiMethodCallExpression call) {
      PsiMethodCallExpression collector =
        tryCast(skipParenthesizedExprDown(call.getArgumentList().getExpressions()[0]), PsiMethodCallExpression.class);
      PsiExpression delimiter;
      if (COLLECTOR_JOINING.test(collector)) {
        return new PsiEmptyExpressionImpl();
      }
      if (COLLECTOR_JOINING_DELIMITER.test(collector)) {
        delimiter = collector.getArgumentList().getExpressions()[0];
        return ExpressionUtils.isSafelyRecomputableExpression(delimiter) ? delimiter : null;
      }
      return null;
    }
@Nullable
    private static PsiExpression extractDelimiter(PsiMethodCallExpression call)