IsNull built-in function

It would be nice to have built-in function acting like SQL IsNull:
    IsNull(value, replacementValue)
    - returns value if it is not null / not default, or replacementValue if value is null / default

Currently, you have to use If like this: Value = If(Value = "", ReplacementValue, Value). In many cases Value and ReplacementValue are fields of entity/structure, which might be a field of other structure, so you know how the expression can be quite long in reality. It would be much clearer, and less chance for mistakes (like when you accidentally put something else in place of Value inside If) with IsNull function.