1. Make changes to some files
2. git add, then git commit them
3. Use git cl upload --gerrit
4. Observe that you get the following error message:
        Upload upstream branch <branch> first.
        Note: maybe you've uploaded it with --no-squash.
              If so, then re-upload it with: git cl upload --squash

Doing this without --gerrit seems to work fine. --no-squash does not help either.