Don't use String8::empty am: fed7d54dfc

Original change: https://android-review.googlesource.com/c/platform/hardware/interfaces/+/2707753

Change-Id: I06ef821e40de1fb7940086cc3cfdfe22a6b47410
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>