[WIP] Undefined variable value yields '.' as node and may cause removing all files in tree.

[bdbaddog]

Fixes #2801. Undefined variable value yields '.' as node and may cause removing all files in tree.

Contributor Checklist:

• [ ] I have created a new test or updated the unit tests to cover the new/changed functionality.
• [x] I have updated CHANGES.txt (and read the README.rst)
• [ ] I have updated the appropriate documentation

[mwichmann]

Attaching a test case made from the original report (suffixed .txt instead of .py due to github limitations)

issue2801.txt