[buildcff2vf] fails for project w/o explicit stat table

[frankrolf]

I have a FDK exercise with a very simple design space – weight axis 0 – 1000, single instance. No STAT-specific sidecar files.
Unfortunately, buildcff2vf fails with the following traceback:

Reading source fonts...
Building variable OTF (CFF2) font...
Validating STAT axis values...
Traceback (most recent call last):
  File "/Users/fgriessh/.pyenv/versions/3.7.4/bin/buildcff2vf", line 8, in <module>
    sys.exit(main())
  File "/Users/fgriessh/.pyenv/versions/3.7.4/lib/python3.7/site-packages/afdko/buildcff2vf.py", line 590, in main
    validate_stat_values(varFont)
  File "/Users/fgriessh/.pyenv/versions/3.7.4/lib/python3.7/site-packages/afdko/buildcff2vf.py", line 409, in validate_stat_values
    if hasattr(stat.table.AxisValueArray, "AxisValue"):
  File "/Users/fgriessh/.pyenv/versions/3.7.4/lib/python3.7/site-packages/fontTools/ttLib/tables/otBase.py", line 555, in __getattr__
    raise AttributeError(attr)
AttributeError: AxisValueArray

Test project here (just run buildcff2vf -d Exercise2.designspace):
cff2vf stat issue.zip