I am not aware about OBIEE,
But if you have sql query then try like this...
replace('Test Data have dots.test','.',' ')
Try the below mentioned formula.
REPLACE("Service Request"."SR#", '.','NULL')
You can use a CASE statement to search for the "." values and to replace with a NULL.
If this is going to be a standard across all reports, then you shold look at moving this logic to rpd or better still, to ETL
OBIEE Replace function for Null values
Change <COLUMN> for your presentation column