Still a week-end question for tired persons.
It is an easy question to reply as soon as you know that a variable declared thru the Declare statement is always initialized to a null value when it is not initialized inside the Declare or by a SET statement ( before its 1st use.
I recognize that I have forgotten this "special" way of initialization up to a session of SQL Server Days related to the basics of T-SQL I participated for the release of SQL Server 2008 R2. As it is now anchored in my memory , the choice was easy. A prof that even a basic session can be useful for a man who began with SQL Server 6.5. Since I have used nearly all versions except the 7.0 . I have to recognize that I am using T-SQL but it is not my favorite topic.
Anyway , thanks for this easy question which permits to dig deeply inside my old memory.