Apparently those page IDs simply don’t exist, and this TypeError happens with any nonexistent page ID, e.g. Special:EntityData/M4 or M13.

This is a specific instance of T272518: Watch for extensions broken by WikiPage now deprecating construction on bad titles. Just needs a check before execution, but eh.

Ah, I wondered why it only started happening recently. Thanks.

Not sure what to do here, to be honest. EntityContentFactory::getTitle() is allowed to return null, according to the interface it implements:

interface EntityTitleLookup {

	/**
	 * Returns the Title for the given entity.
	 *
	 * If the entity does not exist, this method will return either null,
	 * or a Title object referring to a page that does not exist.
	 *
	 * @todo change this to return a TitleValue
	 *
	 * @param EntityId $id
	 *
	 * @throws MWException
	 * @throws OutOfBoundsException
	 * @throws InvalidArgumentException
	 * @return Title|null
	 */
	public function getTitleForId( EntityId $id );

But just changing the return type wouldn’t fix this issue, because the callers in EntityDataUriManager and EntityDataRequestHandler expect this method to return a non-null Title that they can call getFullURL() on, to redirect the request to that URL. I’m guessing this used to work out by redirecting to index.php?curid=<nonexistent>, and we can’t do that anymore.

This also happens if the URL ends in .html, by the way, because that also triggers content negotiation. With other formats, such as .json, it correctly shows an error message that no such entity exists.

I suppose EntityDataUriManager and EntityDataRequestHandler need to be taught that not every entity type can always redirect to a wiki page for a certain entity.

@CBogen @MarkTraceur can your team take care of this issue, since it seems to only affect Structured Data on Commons? (Apologies if I’m pinging the wrong people.)

In T273506#6795550, @Lucas_Werkmeister_WMDE wrote:

@CBogen @MarkTraceur can your team take care of this issue, since it seems to only affect Structured Data on Commons? (Apologies if I’m pinging the wrong people.)

Thanks @Lucas_Werkmeister_WMDE. We'll put it through our normal estimation and prioritization process.

Estimating as medium, but if investigation goes beyond a medium effort, we will re-evaluate.

The problem is that MediaInfoHandler::getTitleForId is declared (and can) return null, but the parent EntityHandler::getTitleForId is not declared to return null.
That means all the code depending on EntityHandler like the EntityContentFactory does not handle the null and failing.

What for a Title could be created to fall back for non-existing MediaInfoIds?
Or should EntityHandler::getTitleForId allow null? It is not the implementation for EntityTitleLookup::getTitleForId which allows null, because EntityHandler is not a lookup, even it is mention with @see in that function.

I suspect the correct solution within MediaInfoHandler::getTitleForId would probable be to throw an InvalidArgumentException in case there's no title for the given id (EntityHandler::getTitleForId is documented to throw that exception if $id refers to an entity of the wrong type.)

That, and whatever code path (EntityDataUriManager::getDocTitle?) currently ends up calling it with such invalid entity id should probably be be updated to catch that exception (or not allow triggering it in the first place) and handle it more gracefully (unless that exception is already being caught, but the TypeError prevents it from getting there)

Change 667684 had a related patch set uploaded (by Umherirrender; owner: Umherirrender):
[mediawiki/extensions/Wikibase@master] Fix null return type hint for EntityContentFactory::getTitleForId

https://gerrit.wikimedia.org/r/667684

Change 667685 had a related patch set uploaded (by Umherirrender; owner: Umherirrender):
[mediawiki/extensions/WikibaseMediaInfo@master] Fix return type for MediaInfoHandler::getTitleForId

https://gerrit.wikimedia.org/r/667685

Patches LGTM, but I didn't +2 the one in Wikibase repo (so that WMDE can look it over & approve)
If they prefer me to +2, LMK, would be happy to.

Change 667684 merged by jenkins-bot:
[mediawiki/extensions/Wikibase@master] Fix null return type hint for EntityContentFactory::getTitleForId

https://gerrit.wikimedia.org/r/667684

Change 667685 merged by jenkins-bot:
[mediawiki/extensions/WikibaseMediaInfo@master] Fix return type for MediaInfoHandler::getTitleForId

https://gerrit.wikimedia.org/r/667685