Use String.Join for concatenation

Encounter this during work in Napier and it is worth to mark it down. People may in favor of using LINQ aggregate method over List<string> but result in performance issue especially when the list is large.

Use String.Join(“, ”, stringArr) instead will do the trick instead of stringArr.Aggregate( (current, next) => current + “, ” + next) since it is not using a string builder.