In c4797fe98655b3d52d0a90ba44fce6e053db3b8b JGit fixes its reachability check
bug which caused the "missing tree ..." error under some circumastances.
Unfortunately, this JGit fix also introduces performance issues for some larger repositories.
To address the performance issue we could try a different approach:
- fall back to the old behavior in JGit (as it was before the c4797fe98655b3d52d0a90ba44fce6e053db3b8b)
- in case we detect a (potentially) unreachable object perform additional (potentially expensive) checks
to verify that it is really unreachable