report prompt date in between clause

Hi ,

I have a ORACLE date column BO_DATE on which a filter needs to be created in the WEBI report.

There will a date prompt P1 on the report .I have a logic on the prompt so that if the user passes NULL(leaves the prompt blank), P1 should have value sysdate-7.

The WHERE condition on the report query should be as follows:

     BO_DATE BETWEEN  P1 and (P1 +4)

where P1 can be either user prompt date or  SYSDATE -7 if user leaves prompt blank.

ie,

BO_DATE BETWEEN NVL(P1,sysdate-7) AND (NVL(P1,sysdate-7) +4)

Whats the best way to handle this condition?

Regds,

Samson