SAP BW query restriction

HI Experts,

in BW query, I am using Latest posting date ( it will give only the latest Posting date ) as a key-figure which is derived from the filed Posting date. However the query is restricted by User selection variable which is customer exit variable :- first date of the month to last date of the Month.

Now my issues if the posting is not happened in the user selected period  means the Latest posting date field was empty.

for example:-

User selected Period

01.06.2016 to 30.06.2016 if there is no posting happened in the this window means the latest Posting date field was empty.

But my requirement is

the Latest posting date should be display the date even if there is not posting happened in the window.

So there is any thing I can do in CKF or RKF, by posting date less than or equal to user input variable.

please guide me on this issues.