Steps to reproduce:

1. Go to https://test.wikidata.org/wiki/Wikidata:Test
2. Open the sidebar widget to make a connection with another page.
3. Enter "de" as the language and "Wikipedia:Spielwiese" as the page
4. Confirm.

Expected: You get an error message explaining that there's a conflict between https://test.wikidata.org/wiki/Q59498 and https://test.wikidata.org/wiki/Q59499 (both link to "commonswiki").

Actual: see the screenshot. There's "Error: $1", which indicates a problem.