Null, <> and blank in set analysis

[#1]

Hi community,

I need to create a expression like following:

=count({<TransDate = {"$(=Date(today()-7,'YYYY-MM-DD'))"}, CustID={Null()}, Product=-{'north'}, Key={' '}>} DISTINCT movieID)

The problem is that the expression doesn't work successfully. How do I solve:

CustID={Null()} - the field should be equal to null.

Product=-{'north'} - the filed should be <>.

Key={' '} - the field should be 'blank'.

Thanks for replay!