PsiExpression (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; }