Create a bad repo that contains a folder named '.git'

gistfile1.scala

      implicit val repo = unpackRepo("/sample-repos/example.git.zip")
      implicit val (revWalk, reader) = repo.singleThreadedReaderTuple

      val inserter = repo.newObjectInserter()

      val badTree = Tree(Seq(Tree.Entry(".git", FileMode.TREE, abbrId("8d28f5"))))
      val badTreeId = badTree.formatter.insertTo(inserter)

      val treeContainingBadTree = Tree(Seq(Tree.Entry("foo", FileMode.TREE, badTreeId)))
      val treeContainingBadTreeId = treeContainingBadTree.formatter.insertTo(inserter)

      val originalCommit = Commit(abbrId("475d").asRevCommit)
      val badCommit = originalCommit.copy(arcs = originalCommit.arcs.copy(tree = treeContainingBadTreeId))
      val badCommitId = inserter.insert(OBJ_COMMIT, badCommit.toBytes)
      val refUpdate = repo.getRefDatabase.newUpdate("refs/heads/master", false)
      refUpdate.setNewObjectId(badCommitId)
      refUpdate.setForceUpdate(true)
      println(s"bad commit ${badCommitId.name}")
      val boom = refUpdate.update()
      println(boom)