While doing a code review I came across an expression isnull(), In first instance I thought this is a typo and space has been missed, but it passed all the test cases.

So what’s the difference between isnull() and “is null”

is null

is null only checks if the value is null
example - select * from students where name is null

isnull()

isnull checks if a value is null and also if it contains empty value.