On 4xx we have to return an empty response instead of an exception

server/extension/sql/80_isolines_helper.sql

@@ -42,6 +42,7 @@ RETURNS SETOF cdb_dataservices_server.isoline AS $$
       return result
     else:
       quota_service.increment_empty_service_use()
+      return []
   except BaseException as e:
     import sys, traceback
     type_, value_, traceback_ = sys.exc_info()