TypeError: 'NoneType' object has no attribute '__getitem__'

[zopyx]

Plone 5.0.5, plone.app.content 3.1.1

A DX content type with

class IPublication(model.Schema):

    connectors = RelationList(
        title=u"Connectors",
        default=[],
        value_type=RelationChoice(title=_(u"Connectors"),
                                  source=ObjPathSourceBinder()),
        required=True,
    )

leads to the following error as soon as you enter something into the auto-complete widget.

2016-08-25 13:55:47 ERROR Zope.SiteErrorLog 1472126147.580.27364738339 http://dev.zopyx.com:12020/Plonewqeqwe/foo/@@edit/++widget++form.widgets.connectors/@@getSource
Traceback (innermost last):
  Module ZPublisher.Publish, line 138, in publish
  Module ZPublisher.mapply, line 77, in mapply
  Module ZPublisher.Publish, line 48, in call_object
  Module plone.app.content.browser.vocabulary, line 217, in __call__
TypeError: 'NoneType' object has no attribute '__getitem__'

> self.parsed_query
> {'sort_on': u'sortable_title', 'sort_order': 'ascending', u'SearchableText': {'query': u'co*'}}
> len(results)
> 0

[gyst]

Confirmed on Plone 5.0.6 with plone.app.content 3.2.

The TypeError is raised when the following line tries to slice the path from val when val is None: https://github.com/plone/plone.app.content/blob/master/plone/app/content/browser/vocabulary.py#L220

I'm using a vanilla RelationChoice configured per the docs at
http://docs.plone.org/external/plone.app.dexterity/docs/advanced/references.html

@provider(IFormFieldProvider)
class ISectionReference(form.Schema):
    """A News Item reference to a news section, instead of containment.
    """

    section = RelationChoice(
        title=_(u"Section"),
        source=ObjPathSourceBinder(
            object_provides=INewsSection.__identifier__),
        required=False,
    )

The @getSource view on the widget works fine, even though this is where the log exception appears to come from; on direct call it returns:
{"total": 2, "results": [{"text": "Company News", "id": "/news/company-news"}, {"text": "Press Mentions", "id": "/news/press-mentions"}]}

[gyst]

Update: on inspection it turns out the TypeError is thrown when the widget queries for the path attribute:

@@getSource?query={"criteria":[{"i":"SearchableText","o":"plone.app.querystring.operation.string.contains","v":"com*"},{"i":"path","o":"plone.app.querystring.operation.string.path","v":"/news/company-news::1"}],"sort_on":"sortable_title","sort_order":"ascending"}&attributes=["UID","Title","portal_type","path","getURL","getIcon","is_folderish","review_state"]&batch={"page":1,"size":10}&_=1475311112907

[gyst]

Fix: replace ObjPathSourceBinder with CatalogSource.

from plone.app.vocabularies.catalog import CatalogSource

@provider(IFormFieldProvider)
class ISectionReference(form.Schema):
    """A News Item reference to a news section, instead of containment.
    """

    section = RelationChoice(
        title=_(u"Section"),
        source=CatalogSource(
            object_provides=INewsSection.__identifier__),
        required=False,
    )

This is a known documentation bug: plone/plone.app.dexterity#200