Apply suggestions from code review

Co-authored-by: Katie Mazaitis <[email protected]>

Author: sgratzl

src/server/endpoints/covidcast.py

@@ -380,7 +380,7 @@ def handle_export():
     if geo_values != "*":
         geo_values = geo_values.split(",")
 
-    as_of, is_as_of_day = parse_day_or_week_arg('as_of') if 'as_of' in request.args else None, is_day
+    as_of, is_as_of_day = parse_day_or_week_arg('as_of') if 'as_of' in request.args else (None, is_day)
     if is_day != is_as_of_day:
         raise ValidationFailedException("mixing weeks with day arguments")