gaudirun argument all-opts produces empty output with GaudiConfig2

When using GaudiConfig2-based options, running gaudirun.py -o opts.py --all-opts <options> produces an empty opts.py file.

$ gaudirun.py GaudiExamples.TestConfig2:main -o opts.py -n --all-opts
# setting LC_ALL to "C"
# ERROR: Some properties are set in old and new style configuration
# WARNING: name: old -> new
# WARNING: ApplicationMgr.AppName: "LHCb" -> 'ApplicationMgr'
$ cat opts.py
$

Omitting --all-opts produces the (non-default) options dump.

$ gaudirun.py GaudiExamples.TestConfig2:main -o opts.py -n
# setting LC_ALL to "C"
$ cat opts.py
{'ApplicationMgr': {'AppName': 'LHCb',
                    'AppVersion': 'v52r1',
                    'EvtMax': 50000,
                    'EvtSel': 'NONE',
                    'ExtSvc': ['Gaudi::Monitoring::MessageSvcSink'],
                    'HistogramPersistency': 'ROOT',
                    'MessageSvcType': 'MessageSvc',
                    'TopAlg': ['GaudiHistoAlgorithm/SimpleHistos']},
 'AuditorSvc': {'Auditors': ['ChronoAuditor']},
 'HistogramDataSvc': {'Input': ["InFile DATAFILE='../data/input.hbook' TYP='HBOOK'"],
                      'OutputLevel': 2},
 'MessageSvc': {'OutputLevel': 3},
 'RootHistSvc': {'OutputFile': 'histo-c2.root'},
 'SimpleHistos': {'HistoPrint': True, 'OutputLevel': 2}}

/cc @clemenci