iter_observations yields tuples with data and error

1 job for master in 1 minute and 30 seconds (queued for 3 minutes)
Status Job ID Name Coverage
  Test
failed #66004
ioke-shell triggered
validate

00:01:30

 
Name Stage Failure
failed
validate Test
    load_entry_point('dbnomics-data-model', 'console_scripts', 'dbnomics-validate')()
File "/home/gitlab-runner/builds/U7X9hszf/0/dbnomics/dbnomics-data-model/dbnomics_data_model/validate_storage.py", line 135, in main
max_series=args.max_series, max_observations=args.max_observations)
File "/home/gitlab-runner/builds/U7X9hszf/0/dbnomics/dbnomics-data-model/dbnomics_data_model/validate_storage.py", line 649, in validate_series
series_id_str = dataset_dir.series_id_str(series_code)
File "/home/gitlab-runner/builds/U7X9hszf/0/dbnomics/dbnomics-data-model/dbnomics_data_model/storages/abstract.py", line 247, in series_id_str
return "/".join(self.series_id(series_code))
TypeError: sequence item 2: expected str instance, NoneType found
ERROR: Job failed: exit status 1