Whenever I introduce a bug that could have been caught automatically I either add the missing unit test or I add a new git hook (there is of course a hook to run unit tests). From missing license files, build failures, to just spelling mistakes in the commit message there is no reason for these to exists in the repository.

I created https://github.com/icefox/git-hooks to manage hooks across repositories, users, and system wide. For example if in a project I add a new hook making sure I never commit an invalid xml file, all repos that have xml files will get the hook for free.