cg-commit doesn't like new repository

I just decided to make a repository of /etc, but because I didn't want to load in all the files, I used git-init-db to create the repository rather than cg-init-db

I then did cg-add for fstab

followed up by cg-commit which then failed as shown below

As soon as I have done a git-commit, all is OK, and cg-commit works again.

I presume there is something that cg-init-db does which makes it suitable for cogito - but what, and shouldn't cg-commit notice and either do it automatically or give a different error message?

cg-commit
usage: git-diff-index [-m] [--cached] [<common diff options>] <tree-ish> 
[<path>...]
common diff options:
  -z            output diff-raw with lines terminated with NUL.
  -p            output patch format.
  -u            synonym for -p.
  --name-only   show only names of changed files.
  --name-status show names and status of changed files.
  -R            swap input file pairs.
  -B            detect complete rewrites.
  -M            detect renames.
  -C            detect copies.
  --find-copies-harder
                try unchanged files as candidate for copy detection.
  -l<n>         limit rename attempts up to <n> paths.
  -O<file>      reorder diffs according to the <file>.
  -S<string>    find filepair whose only one side contains the string.
  --pickaxe-all
                show all files diff when -S is used and hit is found.

cg-commit: Nothing to commit root@kanger etc[master]#