SAP BO Measure IS NULL function

Hi,

When i give the following line is SQL Server

SELECT SALE_TOTAL, DAYS_RENTED FROM SALE WHERE DAYS_RENTED IS NULL

the result is

SALE_TOTAL     DAYS_RENTED

201545.15          NULL

14785.15            NULL

but same line in IDT is invalid

select SALE.SALE_TOTAL from SALE where SALE.DAYS_RENTED IS NULL

what function should i use in where clause to get same result.