Return empty list when prefix is not matched in suggest

Prior to this fix the code was returning a GroupReference with
a `null` group UUID when no matches were found for the prefix.

Having a `null` UUID can cause NPE later on in the code.

Issue: Bug 16571
Change-Id: I414154c50dc0530dad817f1a8291c6bf0ecd7a35
2 files changed
tree: ebd11c34f279e04990cec18b22132aa072fdf6f1
  1. example-setup/
  2. src/
  3. .gitignore
  4. BUILD
  5. Jenkinsfile
  6. LICENSE