The above solutions should work fine, baring in mind that the operators are case sensitive as pointed out by Tne. So in general to filter null values you can use:
- $filter=(SALE_PRICE+ne+null)
- or $filter=not(SALE_PRICE+eq+null)
However in the particular case of SAP HANA analytic views the null value is not supported, as a workaround the filters can be defined on the table column at the modeling level of the analytic view. The solution is explained here.