Computed Sample Field "SampleTypeUID" does not check if a SampleType is set

[ramonski]

Steps to reproduce

Accessing the Sample on it's own, e.g. over the API v2 (/@@API/v2/sample/<UID>) fails if now SampleType is set and the accessor getSampleTypeUID is called.

Current behavior

The following Traceback occurs:

Traceback (most recent call last):
  File "/Users/rbartl/develop/ridingbytes/bika/buildout/eggs/plone.jsonapi.core-0.6-py2.7.egg/plone/jsonapi/core/browser/decorators.py", line 24, in decorator
    return f(*args, **kwargs)
  File "/Users/rbartl/develop/ridingbytes/bika/buildout/eggs/plone.jsonapi.core-0.6-py2.7.egg/plone/jsonapi/core/browser/api.py", line 60, in to_json
    return self.dispatch()
  File "/Users/rbartl/develop/ridingbytes/bika/buildout/eggs/plone.jsonapi.core-0.6-py2.7.egg/plone/jsonapi/core/browser/api.py", line 54, in dispatch
    return router(self.context, self.request, path)
  File "/Users/rbartl/develop/ridingbytes/bika/buildout/eggs/plone.jsonapi.core-0.6-py2.7.egg/plone/jsonapi/core/browser/router.py", line 138, in __call__
    return self.view_functions[endpoint](context, request, **values)
  File "/Users/rbartl/develop/ridingbytes/bika/buildout/src/bika.lims/bika/lims/jsonapi/v2/routes/content.py", line 97, in search
    return api.get_batched()
  File "/Users/rbartl/develop/ridingbytes/bika/buildout/src/bika.lims/bika/lims/jsonapi/api.py", line 79, in get_batched
    complete=complete)
  File "/Users/rbartl/develop/ridingbytes/bika/buildout/src/bika.lims/bika/lims/jsonapi/api.py", line 1393, in get_batch
    endpoint, complete=complete),
  File "/Users/rbartl/develop/ridingbytes/bika/buildout/src/bika.lims/bika/lims/jsonapi/api.py", line 234, in make_items_for
    return map(extract_data, brains_or_objects)
  File "/Users/rbartl/develop/ridingbytes/bika/buildout/src/bika.lims/bika/lims/jsonapi/api.py", line 229, in extract_data
    info = get_info(brain_or_object, endpoint=endpoint, complete=complete)
  File "/Users/rbartl/develop/ridingbytes/bika/buildout/src/bika.lims/bika/lims/jsonapi/api.py", line 273, in get_info
    info.update(adapter.to_dict())
  File "/Users/rbartl/develop/ridingbytes/bika/buildout/src/bika.lims/bika/lims/jsonapi/dataproviders.py", line 52, in to_dict
    data = self.extract_fields()
  File "/Users/rbartl/develop/ridingbytes/bika/buildout/src/bika.lims/bika/lims/jsonapi/dataproviders.py", line 89, in extract_fields
    fieldvalue = dm.json_data(fieldname)
  File "/Users/rbartl/develop/ridingbytes/bika/buildout/src/bika.lims/bika/lims/jsonapi/datamanagers.py", line 171, in json_data
    return fieldmanager.json_data(self.context)
  File "/Users/rbartl/develop/ridingbytes/bika/buildout/src/bika.lims/bika/lims/jsonapi/fieldmanagers.py", line 258, in json_data
    value = self.get(instance)
  File "/Users/rbartl/develop/ridingbytes/bika/buildout/src/bika.lims/bika/lims/jsonapi/fieldmanagers.py", line 204, in get
    return self._get(instance, **kw)
  File "/Users/rbartl/develop/ridingbytes/bika/buildout/src/bika.lims/bika/lims/jsonapi/fieldmanagers.py", line 253, in _get
    return self.field.get(instance)
  File "/Users/rbartl/develop/ridingbytes/bika/buildout/eggs/Products.Archetypes-1.9.13-py2.7.egg/Products/Archetypes/Field.py", line 2156, in get
    return eval(self.expression, {'context': instance, 'here': instance})
  File "<string>", line 1, in <module>
AttributeError: 'NoneType' object has no attribute 'UID'

Expected behavior

The computed field reurns None