Merging is not possible because you have unmerged files.
error: Merging is not possible because you have unmerged files.
hint: Fix them up in the work tree, and then use 'git add/rm '
hint: as appropriate to mark resolution and make a commit.
fatal: Exiting because of an unresolved conflict.
Thank you Linus Torvalds for these wonderful errors !
This can happen when you push a branch, do a pull request back to master using a web-based tool such as Stash or Githhub, then go back to your branch, do more commits and push, then do again a pull request and notice that the web-based tool is trying to merge back again all your changes, even the ones already merged. So you merge master into your branch to actualize it then are hit with merge conflicts and if you try to go back to master you'll get this crap.
Don't do that.
$ git merge --abort