NULL in where of a filter stage

[ds_is_fun]

What syntax do i throw in a filter stage while looking for a NULL value in a specific column.
IsNull(Col)
OR
??
Thx

[throbinson]

Parallel Developer's Guide Chapter 29-4 (page654)

Testing for a Null
You want to test column serialno to see if it contains a null. If it does,
you want to write the corresponding records to the output link.
You enter the following in the Where property:
serialno is null

or
is not null