If you visit /browser/this_path_does_not_exist, the following traceback will occur using the 0.10 plugin (0.11 with its respective plugin shows the correct "No node" error).
Traceback (most recent call last):
File "/home/tim/code/trac-0.10.3.1/trac/web/main.py", line 387, in dispatch_request
File "/home/tim/code/trac-0.10.3.1/trac/web/main.py", line 237, in dispatch
File "/home/tim/code/trac-0.10.3.1/trac/versioncontrol/web_ui/browser.py", line 145, in process_request
File "/home/tim/code/trac-0.10.3.1/trac/versioncontrol/web_ui/browser.py", line 246, in _render_file
File "/home/tim/tmp/gitplugin/0.10/gitplugin/git_fs.py", line 97, in get_changeset
return GitChangeset(self.git, rev)
File "/home/tim/tmp/gitplugin/0.10/gitplugin/git_fs.py", line 237, in __init__
(msg,props) = git.read_commit(sha)
File "/home/tim/tmp/gitplugin/0.10/gitplugin/PyGIT.py", line 76, in read_commit
raw = self._git_call("git-cat-file commit "+sha)
TypeError: cannot concatenate 'str' and 'NoneType' objects
Noticed in the wild on all demo environments linked, and verified against 0.10.3.1 and the latest git plugin from http://trac-hacks.org/svn/gitplugin/0.10 today.