KF default types

I have a KF that I am calculating while loading the data ie in the update rules.

but in some cases the business wants this to be blank when a particular IO in the source is initial.

For this how should my KF be defined. I have defined it as integer. but in the update routine even when I say RESULT = ' '. , I see the value update as 0. Cant an integer be left blank. Theres no problem with the code.

Help needed !!