Just like you said
select * from tbl where statusid is null
or
select * from tbl where statusid is not null
If your statusid is not null, then it will be selected just fine when you have an actual value, no need for any “if” logic if that is what you were thinking
select * from tbl where statusid = 123 -- the record(s) returned will not have null statusid
if you want to select where it is null or a value, try
select * from tbl where statusid = 123 or statusid is null