Interesting question, but when i execute bit modified this script, i receive other error:

declare

@decimal decimal(18,6),

@bit bit,

@float float,

@integer int,

@money money

select IsNull(@decimal, '')

select isnull(@bit, '')

select isnull(@integer, '')

select isnull(@money, '')

select isnull(@float, '')

So error was next:

Msg 257, Level 16, State 3, Line 11

Implicit conversion from data type varchar to money is not allowed. Use the CONVERT function to run this query.

I responded to this question as script will fail for SELECT IsNULL(@money, ''), but my answer is wrong 🙁