- Go to https://www.wikidata.org/wiki/Q1057968?debug=1&uselang=en
- Click on "add" to add a new "subclasse of" property
- Add "Q21083858" to the field
- Click on "Add reference"
{ "errorMessage": "Uncaught Error: Required option not specified properly", "url": "https://www.wikidata.org/static/1.27.0-wmf.3/extensions/Wikidata/extensions/Wikibase/view/resources/jquery/wikibase/jquery.wikibase.referenceview.js", "lineNumber": 108, "columnNumber": 4, "errorObject": {} }
- Attempt to "save" anyway
{ "errorMessage": "Uncaught TypeError: Cannot read property 'getButton' of undefined", "url": "https://www.wikidata.org/static/1.27.0-wmf.3/extensions/Wikidata/extensions/Wikibase/view/resources/jquery/wikibase/toolbar/controller/definitions/edittoolbar/referenceview.js", "lineNumber": 73, "columnNumber": 26, "errorObject": {} }