Merge branch 'stable-2.13'

* stable-2.13:
  Compile against Gerrit 2.13.9
  Remove usage of java.util.Optional

"Remove usage of java.util.Optional" is reverted in this merge, this
commit was only needed on stable-2.13 branch.

Change-Id: I9220a5fdf443f8537aa58b23491c37c6b6b58e79
tree: 3cbaff26c15a4cabe0d011b6dc8b2eb5685ce787
  1. .settings/
  2. src/
  3. .gitignore
  4. BUILD
  5. LICENSE