When doing repoman commit, if you decide you want to bail out and say empty out the commit message editor. Repoman continues with the commit and just adds the portage signature. Despite an empty commit message. In the event of an empty commit message, repoman should bail and fail to commit as git would if you typed nothing in the editor.
repoman support has been removed per bug 835013. Please file a new bug (or, I suppose, reopen this one) if you feel this check is still applicable to pkgcheck and doesn't already exist.