Filter unassigned values in report output

Hi Friends,

I have a requirement as explained below.

There is a variable for Document Number with Select Options in the selection screen.

There are some documents which come as unassigned in BW, When I execute the query leaving this document no field blank it picks up all the blank document nos also and displays them as # unassigned.

I had tried by excluding # in the variable default value and also by Do NOt Include in selection in the query Designer, but it goes for a toss if the user changes in the Selection screen or removes the filter value in the Query Output.

Is there any way we can achieve following:

1. Even if user leaves this Variable as Blank, the report should filter out the # values.

2. If in case user enters # over there, report should not bring any output.

Objective is to hide the # Document Nos and user should not have any option to change in the query output.

can it be done by doing something in Variable exit or is there any other way.

would appreciate your help.

Regards

Deepak