Fix unit-test

:Release Notes:
Fix 'test_transport_message' to check for '(null)'
service name instead of empty string.

:Detailed Notes:

:Testing Performed:
Unit-tests.

:QA Notes:

:Issues Addressed:
[ANG-5035] ls-monitor compact mode does not catch method call from luna-send

Open-webOS-DCO-1.0-Signed-off-by: Alexandr Smoktal <alexandr.smoktal@lge.com>

Change-Id: I32e0e8116934c89813b62ce7bfb0386f584be30b
Reviewed-on: https://g2g.palm.com/5173
Reviewed-by: DCO Verification
Reviewed-by: Alexandr Smoktal <alexandr.smoktal@lge.com>
Tested-by: Alexandr Smoktal <alexandr.smoktal@lge.com>
Reviewed-by: Anatolii Sakhnik <anatolii.sakhnik@lge.com>