GitRepositoryReader(@NotNull File gitDir) {
   myGitDir = gitDir;
   assertFileExists(myGitDir, ".git directory not found in " + gitDir);
   myHeadFile = new File(myGitDir, "HEAD");
   assertFileExists(myHeadFile, ".git/HEAD file not found in " + gitDir);
   myRefsHeadsDir = new File(new File(myGitDir, "refs"), "heads");
   myRefsRemotesDir = new File(new File(myGitDir, "refs"), "remotes");
   myPackedRefsFile = new File(myGitDir, "packed-refs");
 }