if (branch == null)
throw new RefNotFoundException(MessageFormat.format(JGitText
.get().refNotResolved, name));
RevWalk revWalk = new RevWalk(repo);
AnyObjectId headId = headRef.getObjectId();
RevCommit headCommit = headId == null ? null : revWalk
.parseCommit(headId);
RevCommit newCommit = revWalk.parseCommit(branch);
RevTree headTree = headCommit == null ? null : headCommit.getTree();
DirCacheCheckout dco = new DirCacheCheckout(repo, headTree,