excluding null values in set analysis

[ali_hijazi]

Hello

I have an expression in which I want to calculate the sum of a field without taking into consideration the null values as follows:

sum (
       {$<
       Type={Sales},
       PeriodDate={"<=$(=vPeriodDate) >=$(=vCurrentYearStart)"},

          Emp_name -= {$(=null())}
       >}
       Sales$HT
       )

however I'm getting error in expression syntax; check attached

[SunilChauhan]

sum (
       {$<
       Type={Sales},
       PeriodDate={"<=$(=vPeriodDate) >=$(=vCurrentYearStart)"},

          Emp_name -= {}
       >}
       Sales$HT
       )

hope this helps