I have no idea how a missingparam error could be flaky, surely we’re always calling the API with a consistent set of parameters…

Other failed builds:

• 2026-02-02

Noting that this is still seen, e.g. on this CI build for this ConfirmEdit patch.

The screenshot of that build looks slightly different than in the task description:

{
  "errors": [
    {
      "code": "missingparam",
      "module": "wbformatvalue",
      "*": "The \"datavalue\" parameter must be set."
    }
  ],
  "servedby": "mw-api-ext.eqiad.main-66467fdf7d-t9fn9",
  "*": "See https://www.wikidata.org/w/api.php for API usage. Subscribe to the mediawiki-api-announce mailing list at <https://lists.wikimedia.org/postorius/lists/mediawiki-api-announce.lists.wikimedia.org/> for notice of API deprecations and breaking changes."
}

So we’re somehow sending a request with no datavalue at all to action=wbformatvalue.

Aha, TIL JSON.stringify( undefined ) returns undefined. So when we have

	const params = {
		action: 'wbformatvalue',
		generate: generate,
		datavalue: JSON.stringify( dataValue )
	};

the datavalue is undefined and mw.Api strips it out. So we just™ need to make sure not to pass undefined values into the renderSnak*() functions.

https://gerrit.wikimedia.org/r/c/mediawiki/core/+/1241256

• https://integration.wikimedia.org/ci/job/quibble-with-Wikibase-extensions-browser-tests-only-vendor-php83/186/console
• https://integration.wikimedia.org/ci/job/quibble-with-Wikibase-extensions-browser-tests-only-vendor-php83/201/console
• https://integration.wikimedia.org/ci/job/quibble-with-Wikibase-extensions-browser-tests-only-vendor-php83/1135/console

The console logs in the Jenkins web UI of these jobs are very confusing, I can only see the failing tests from the plain text view. Two of the above are the same as the description, another one as below:

  Running:  addQualifier.cy.ts                                                             (2 of 12)


  wbui2025 add qualifiers
    mobile view
      ✓ is possible to add and edit a qualifier (14425ms)
    mobile view (wbui2025) - tabular-data qualifier
      1) can add a tabular-data qualifier with lookup
    mobile view (wbui2025) - geo-shape qualifier
      ✓ can add a geo-shape qualifier with lookup (2745ms)
      ✓ shows dropdown menu when typing in geo-shape qualifier lookup (2359ms)


  3 passing (41s)
  1 failing

  1) wbui2025 add qualifiers
       mobile view (wbui2025) - tabular-data qualifier
         can add a tabular-data qualifier with lookup:
     AssertionError: Timed out retrying after 20000ms: Expected to find element: `[data-v-app] .wikibase-wbui2025-edit-link`, but never found it.
      at __webpack_modules__../cypress/support/pageObjects/ItemViewPage.ts.ItemViewPage.editLinks (webpack://wikibase/./cypress/support/pageObjects/ItemViewPage.ts:53:12)
      at Context.eval (webpack://wikibase/./cypress/e2e/wbui2025/addQualifier.cy.ts:205:16)


In T416160#11623630, @Lucas_Werkmeister_WMDE wrote:

The screenshot of that build looks slightly different than in the task description:

But I just noticed something: the API request seen in both screenshots really is invalid!

Also note that there is an invalid API call with value= (empty string) to action=wbparsevalue

In T416160#11712294, @Func wrote:

Also note that there is an invalid API call with value= (empty string) to action=wbparsevalue

Good catch, thanks – that must be where the undefined value to parse comes from, then. (But wbparsevalue doesn’t complain about it because its values= parameter takes a list, unlike wbformatvalue, and it’s okay for the list to be empty. So we only notice the error one API call later.)

Change #1269008 had a related patch set uploaded (by Lucas Werkmeister (WMDE); author: Lucas Werkmeister (WMDE)):

[mediawiki/extensions/Wikibase@master] Make sure parseValue() doesn’t return undefined

https://gerrit.wikimedia.org/r/1269008

Change #1269009 had a related patch set uploaded (by Lucas Werkmeister (WMDE); author: Lucas Werkmeister (WMDE)):

[mediawiki/extensions/Wikibase@master] Don’t make an API call to parse the empty string

https://gerrit.wikimedia.org/r/1269009

Change #1269008 merged by jenkins-bot:

[mediawiki/extensions/Wikibase@master] Make sure parseValue() doesn’t return undefined

https://gerrit.wikimedia.org/r/1269008

Change #1269009 merged by jenkins-bot:

[mediawiki/extensions/Wikibase@master] Don’t make an API call to parse the empty string

https://gerrit.wikimedia.org/r/1269009

The issue seems to be fixed as it didn't occur again, I will mark it as resolved.
(If for some reason, it appeared again, we can reopen this task).
Thank you!