Concat NULL value in SQL Server? TCS Interview Questions

SQL Server interview question asked in TCS interview.

Q: What would be the output of following script?

Ans:

Q: So how you will print FullName as "Vikas Ahlawat"
Ans: I will use ISNULL() function like below

Q: If I not allow to use ISNULL() what would be other solution?
Ans: I will use CONCAT() function (introduced in SQL Server 2012)