Webi Default Date Prompt filter in Universe

Hello,

I am trying to create a default date filter prompt in universe to take in default date ,for scheduling dumps of report daily

below is the oracle sql code(Oracle 12c)

HV_AUM_MGMTFEES.TRANS_DATE =

CASE WHEN 

@Prompt('To Date','DT',

'Hv Aum Mgmtfees\Trans Date',mono,free,Not_Persistent)  is null

THEN

select max(trans_date)+1 from  HV_AUM_MGMTFEES

ELSE

@Prompt('To Date','DT',

'Hv Aum Mgmtfees\Trans Date',mono,free,Not_Persistent)

END

i am getting missing expression error is this the right approach or is there something wrong with the code

Thanks in advance

Gaurav