How do I : export to a dynamic file name?

I want to be able to initialize the file name in a session variable, and then have SS write to that as a file name.

The following doesn't work. I get a file named "null.csv"

Ex Init:
session.setVariable( "PLATFORM", "xbox360" );

Ex Export:
out = new FileWriter( dataRecord.get( "PLATFORM" ) + ".csv", true );

Thanks.

~@DAVE@~