Steps to replicate the issue (include links if applicable):

• Install browser extension Vue.js Devtools
• Get localhost PageTriage working
• Visit http://localhost:8080/wiki/Special:NewPagesFeed
• Open browser console

What happens?:

load.php?lang=en&mod…r&version=1w36o:300
[Vue warn]: Invalid prop: type check failed for prop "modelValue". Expected String | Number | Null | Array, got Undefined  
  at <CdxToggleButtonGroup modelValue=undefined onUpdate:modelValue= 
(2) [ƒ, ƒ]
 buttons= 
(2) [{…}, {…}]
  ... > 
  at <CdxField> 
  at <NppSortDirRadio> 
  at <ListFilterMenu> 
  at <App >

What should have happened instead?:

• no devtools javascript console warnings

Software version (on Special:Version page; skip for WMF-hosted wikis like Wikipedia):

Other information (browser name/version, screenshots, etc.):

• fix may be similar to https://gerrit.wikimedia.org/r/c/mediawiki/extensions/PageTriage/+/1011156