how to assgin the null value

How to assgin null value for a variable or any value
for example
if a=1 then
customerid
else
in else part i need null but default it is taking 0
how to assign valuefor example
if a=1 then
customerid
else

try this

if a=1 then
ToText(customerid)
else
''|||this is not a NULL value, it's a blank string with is not the same. would matter if he is doing counts or anything.

to trully create a null, make a formula called @.NULL and leave it completely BLANK. then reference the formula in the IF-Statement like

IF _______
THEN _______
ELSE {@.NULL}