assign null value to a field in plpgsql

Hello -

I'm using PG 8.2.

I have some code of the form

domain2Row domain2_dom%ROWTYPE;
adServerLoadRow domain2_dom%ROWTYPE;
...
SELECT * INTO domain2Row FROM domain2_dom WHERE domain_name_dom =
quote_literal(domainName);
adServerLoadRow = domain2Row;

I want to go through a series of checks to see if I should set a field to
null in the adServerLoadRow. I will not know in advance which fields I will
need to check nor their data types.

Assuming I have identified field X as one which I want to set to null, I
want to be able to perform the following assignment;

adServerLoadRow.X = NULL;

However, I can't seem to do this. I thought about just declaring a variable
and not assigning anything to it, so it would be null. Then I could do the
following

adServerLoadRow.X = aNullVariable;

The problem is that I won't know in advance whether the field is numeric or
text, so I won't know which null variable to use.

I'm constrained to use plpgsql, so alternate language solutions won't help
me.

Any suggestions would be greatly appreciated.

david