When configuring a free style job with the "Plublish to confluence" build step today we got an error.

The JS console prints errors like

The interessting error is

Legacy checkUrl ''descriptorByName/ConfluencePublisher/pageNameCheck?siteName='+Form.findMatchingInput(this,'siteName').value+'&spaceName='+Form.findMatchingInput(this,'_.spaceName').value+'&pageName='+escape(this.value)' is not valid JavaScript: TypeError: Form.findMatchingInput(...) is undefined 

This points direcly to a recent change replacing Form.findMatchingInput from prototype.js with a pure JS function: https://github.com/jenkinsci/jenkins/pull/8008/

After some more investigation it seems to me that the change in the pull request is not a pure replacement.

The old function called Form.getInputs which returns input, textarea and select elements. The new function replaced it by only looking for input elements (see: https://github.com/jenkinsci/jenkins/pull/8008/files#diff-10922aee3260853be495a09cf3bf13bf5f931bc128e334807e3008ff00b57651L2266)

This causes the call to Form.findMatchingInput(this,'siteName') to return undefinded as "siteName" is a select not an input.

I also tested the behavior with a new installation of 2.405 and 2.406 via docker. 2.405 works, whereas 2.406 does not.