Comment 1 for bug 785377

Probably a duplicate of bug 82555 but the traceback is fun, maybe the recent fix to bug 242175 will help?

Steps to repo:

$ bzr init tmp1
Created a standalone tree (format: 2a)
$ touch tmp1/file
$ bzr add tmp1
adding file
$ bzr commit -m "Adding file" tmp1
Committing to: /.../tmp1/
added file
Committed revision 1.
$ bzr init tmp2
Created a standalone tree (format: 2a)
$ bzr merge -d tmp2 tmp1
+N file
All changes applied successfully.
$ bzr st tmp2
working tree is out of date, run 'bzr update'
renamed:
  file => file
$ bzr update tmp2
bzr: ERROR: exceptions.ValueError: WorkingTree.set_root_id with fileid=None
...