Removing a ref after lefthook install fails to fetch from the main branch

[mrexox]

Summary

When you remove a ref option from remote configuration, and you already had lefthook install-ed, the remote syncing fails.

Steps to reproduce

remote:
  git_url: https://github.com/evilmartians/lefthook
  ref: v1.1.1
  config: examples/complete/lefthook.yml

$ lefthook install
SYNCING
SERVED HOOKS: commit-msg, pre-commit, pre-push
$ git -C .git/info/lefthook-remotes/lefthook/ log --oneline
55f4381 (grafted, HEAD, tag: v1.1.1) 1.1.1: Quote path to script

remote:
  git_url: https://github.com/evilmartians/lefthook
  config: examples/complete/lefthook.yml # assumed to fetch from master branch 

$ lefthook install
SYNCING
SERVED HOOKS: commit-msg, pre-commit, pre-push
$ git -C .git/info/lefthook-remotes/lefthook/ log --oneline
55f4381 (grafted, HEAD, tag: v1.1.1) 1.1.1: Quote path to script # (!) must be master branch

Expected results

Expected to checkout to the main branch of the repository. May be master or main branch at least.

Possible Solution

Provide a default value for the ref.