local variable 'fromId' referenced before assignment

[twekberg]

While running dirtree-chart-0.0.6 with this command line:

python -m dirtree_chart -r . -d TD -md 2

I got this stack trace:

Traceback (most recent call last):
  File "/usr/lib/python3.8/runpy.py", line 194, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/usr/lib/python3.8/runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "/home/tekberg/src/tracker/tracker-env/lib/python3.8/site-packages/dirtree_chart/__main__.py", line 59, in <module>
    main()
  File "/home/tekberg/src/tracker/tracker-env/lib/python3.8/site-packages/dirtree_chart/__main__.py", line 48, in main
    DirStrucTree(root,
  File "/home/tekberg/src/tracker/tracker-env/lib/python3.8/site-packages/dirtree_chart/diagram.py", line 70, in __init__
    self._createLayerHierarchy()
  File "/home/tekberg/src/tracker/tracker-env/lib/python3.8/site-packages/dirtree_chart/diagram.py", line 206, in _createLayerHierarchy
    self._addIdsToLayerHierarchy()
  File "/home/tekberg/src/tracker/tracker-env/lib/python3.8/site-packages/dirtree_chart/diagram.py", line 186, in _addIdsToLayerHierarchy
    folder = "{}__mermaid__{}".format(folder, fromId)
UnboundLocalError: local variable 'fromId' referenced before assignment

If it helps, the output from tree -L 2 is attached.
tree-L-2.txt