default date prompt in dimensional crosstab report

[avuong6]

i have a 4 column report in which users can define the 4 periods for the report. for period 4, i would like it to be optional. so if no selection is made, i would like it to not select a period and then the 4 column report turns into a 3 column report. the prompt for column 4 is currently coded like this:

#prompt('P_Period4', 'memberuniquename' , '' , '' , '[Sales].[Monthly Periods].[Period].[Period]')#

how do i default this to basically not return anything if no selection is made on period 4? is this possible?

[bdbits]

Just make the last prompt optional, then use render variables to hide the 4th column if nothing was chosen.