Exception mentioning index out of range

[cbenz]

Here is a stack trace we receive sometimes by e-mail:

URL: http://api.openfisca.fr/api/1/calculate
Module weberror.errormiddleware:171 in __call__
>>  app_iter = self.application(environ, sr_checker)
Module webob.dec:131 in __call__
>>  resp = self.call_func(req, *args, **self.kwargs)
Module webob.dec:196 in call_func
>>  return self.func(req, *args, **kwargs)
Module openfisca_web_api.application:37 in set_application_url
>>  return req.get_response(app)
Module webob.request:1316 in send
>>  application, catch_exc_info=False)
Module webob.request:1280 in call_application
>>  app_iter = application(self.environ, start_response)
Module openfisca_web_api.urls:115 in router
>>  return app(req.environ, start_response)
Module webob.dec:131 in __call__
>>  resp = self.call_func(req, *args, **self.kwargs)
Module webob.dec:196 in call_func
>>  return self.func(req, *args, **kwargs)
Module openfisca_web_api.controllers.calculate:258 in api1_calculate
>>  )(data['scenarios'], state = ctx)
Module biryani.baseconv:2407 in uniform_sequence_converter
>>  value, error = converter(value, state = state)
Module openfisca_web_api.environment:115 in json_to_cached_or_new_instance
>>  value, state = state or conv.default_state)
Module openfisca_core.scenarios:352 in json_to_instance
>>  value = value, state = state or conv.default_state)
Module openfisca_core.scenarios:285 in json_or_python_to_attributes
>>  )(data, state = state)
Module biryani.baseconv:1781 in structured_mapping_converter
>>  value, error = converter(values.get(name), state = state)
Module openfisca_france.scenarios:80 in json_or_python_to_test_case
>>  menage['personne_de_reference'] = famille['parents'][0]
IndexError: list index out of range

[MattiSG]

Cannot reproduce.