ContentHandlerSanityTest test case testMakeEmptyContent assumes that every content handler can create empty content. Wikibase, however, produces this exception:
MWException: Cannot make an empty EntityContent, since we require at least an ID to be set.
This needs to be reconciled by either removing the assumption on the test or fixing the wikibase content handler to be able to produce it.
Change 337029 had a related patch set uploaded (by Daniel Kinzler):
Support creation of empty entities.
While en empty EntityContent object doesn't make much sense, it's useful to be able to create them e.g. to be able to create diffs consistently. MW core creates empty Content objects in a few places to allow for a consistent code path in the absense of an actual Content object.
Change 338023 had a related patch set uploaded (by Smalyshev):
Check that empty content is valid only on handlers that allow direct editing.
Change 338023 merged by jenkins-bot:
Check that empty content is valid only on handlers that allow direct editing.
Change 356228 had a related patch set uploaded (by Daniel Kinzler; owner: Daniel Kinzler):
[mediawiki/core@master] Allow makeEmptyContent to return null for some kinds of content.
Change 356228 abandoned by Daniel Kinzler:
Allow makeEmptyContent to throw MWException for some kinds of content.