I propose replacing the existing method with the new one.

But it occurred to me after I wrote the comment above that we might be able to replace the method with a smaller variant using the PathFilter code.  The existing PathFilter can mostly do the same thing; add it to the TreeWalk.  setRecursive(false).  Then when tw.isSubtree() is true and the PathFilter is not done, enter the subtree.  The "path filter is not done" part is new, we would need to add that to the PathFilter class to let it see if the TreeWalk's current length is equal to the PathFilter's path length.  If the lengths are the same, we know this is the target.  If TreeWalk's current path is shorter, we know we need to dive into the subtree.

That may be a much cleaner solution because its less code, and we aren't going through this mess of parsing the path ourselves.