--export-json issues AttributeError: 'SameSimTestSuite' object has no attribute 'test_configuration'

[olivierdennewald]

when trying to use export-json with axi_dma example, on 5.0.0.dev7 release, we get the following stacktrace :

]$ python3 /home/oliden2e/github/vunit/examples/vhdl/axi_dma/run.py --export-json EXPORT_JSON
Traceback (most recent call last):
File "/home/oliden2e/.local/lib/python3.6/site-packages/vunit_hdl-5.0.0.dev7-py3.6.egg/vunit/ui/init.py", line 728, in main
all_ok = self._main(post_run)
File "/home/oliden2e/.local/lib/python3.6/site-packages/vunit_hdl-5.0.0.dev7-py3.6.egg/vunit/ui/init.py", line 763, in _main
return self._main_export_json(self._args.export_json)
File "/home/oliden2e/.local/lib/python3.6/site-packages/vunit_hdl-5.0.0.dev7-py3.6.egg/vunit/ui/init.py", line 1099, in _main_export_json
test_configuration = test_suite.test_configuration
AttributeError: 'SameSimTestSuite' object has no attribute 'test_configuration'

Is there a particular way to use this option, or is it just some bug to be fixed ?
thx.
Olivier.