ASP Stored Procedure DATE Default Value

Hello, I'm building an ASP stored procedure to do an insert & then return a recordset,... one of the lines inserts into a date column, what I would like to do is give it a default value of Today -1day if no value is submitted ---

The relevent lines on the SP currently looks like -

Dim CMDProductInsert__availabledate
CMDProductInsert__availabledate = "dat"
if(UploadFormRequest("availabledate") <> "") then CMDProductInsert__availabledate = Server.HTMLEncode(ProtectSQL(UploadFormRequest("availabledate")))

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Where "dat" is where I want the default value to go...

Thanks