AI deck example fails while transferring the neural net to C code

[bot-motion]

It is unclear if the following is a bug in the SDK 3.9.1 or some other problem:

GENERATING NNTOOL STATE FILE
/gap_sdk/tools/nntool/nntool -s model/nntool_script BUILD_MODEL_SQ8BIT/model.tflite 
Traceback (most recent call last):
  File "/gap_sdk/tools/nntool/nntool", line 101, in <module>
    main()
  File "/gap_sdk/tools/nntool/nntool", line 91, in main
    mod = importlib.import_module('interpreter.nntool_shell')
  File "/usr/lib/python3.6/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 994, in _gcd_import
  File "<frozen importlib._bootstrap>", line 971, in _find_and_load
  File "<frozen importlib._bootstrap>", line 955, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 665, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 678, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "/gap_sdk/tools/nntool/interpreter/nntool_shell.py", line 18, in <module>
    from .commands import *
  File "/gap_sdk/tools/nntool/interpreter/commands/qtune.py", line 23, in <module>
    class QtuneCommand(NNToolShellBase):
  File "/gap_sdk/tools/nntool/interpreter/commands/qtune.py", line 51, in QtuneCommand
    required=True)
  File "/usr/local/lib/python3.6/dist-packages/cmd2/argparse_custom.py", line 748, in add_subparsers
    return super().add_subparsers(**kwargs)
  File "/usr/lib/python3.6/argparse.py", line 1716, in add_subparsers
    action = parsers_class(option_strings=[], **kwargs)
TypeError: __init__() got an unexpected keyword argument 'required'
model_rules.mk:64: recipe for target 'BUILD_MODEL_SQ8BIT/model.json' failed
make: *** [BUILD_MODEL_SQ8BIT/model.json] Error 1

Also being discussed here: bitcraze/aideck-gap8-examples#41