Checking null attribute in calcscript

Hello experts,

I have a calc script that I have to check if attribute of specific member is null or not, this is my code but is not working:

FIX(@RELATIVE("Entity",0 ))
FIX (&Act_Year,"Real",@RELATIVE("Total_Customer",0 ))
"Jan"(
IF (NOT(@CalcMgrCompare(@NAME(@ATTRIBUTESVAL("Customer_CB")),@NAME("NULL"), @_false)))
———- Code

ENDIF
)
ENDFIX
ENDFIX

In main FIX I have all the customers, and Customer has Attribute Dimension called "Customer_CB", I need to do some operations if Attribute exists, else I don't have to do nothing.

Any help in calc script? If is possible to groovy I'm open to create groovy script too.