Fix filter clause bug

:Release Notes:
Fix filter clause bug

:Detailed Notes:
 - Applied filtering "" string. Because ICU doesn't support
 - Added unit test code

:Testing Performed:
tested on build

:QA Notes:

:Issues Addressed:
[GF-44120] filter clause does not work well

Open-webOS-DCO-1.0-Signed-off-by: kyouhyun.hwang <kyouhyun.hwang@lge.com>

Change-Id: I12343189a88136ae5867e0b977dada3ed5cf2791
Reviewed-on: https://g2g.palm.com/3748
Reviewed-by: Build Verification
Reviewed-by: Maksym Sditanov <maxim.sditanov@lge.com>
Tested-by: Maksym Sditanov <maxim.sditanov@lge.com>