Set Analysis tricky field comaprision

[smilingjohn]

Hi All, 

With the help of community I am trying to solve or condition in a set analysis which I doubt not giving me the right output . 

Here basically I am trying to compare one field with other along with the using or condition to consider the null defined values . Please have a look at my set analysis expression which don't give any error but even not giving the correct output . 

Count({<Category=P(SubCategory)>+<Category={'null'}>}ID)

Can someone please  help me on this 

Thanks in Advance 

[Taoufiq_Zarra]

@smilingjohn  can you share a sample data and the expected output ?