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

• Import sites using importSites.php
• Create a new item
• Visit the item page

What happens?:

Wikibase\Lib\LanguageNameLookup::getName(): Argument #1 () must be of type string, null given, called in /srv/femiwiki.com/extensions/Wikibase/view/src/SiteLinksView.php on line 301

The full backtrace is here on GitHub

What should have happened instead?:

The item page should be open.

Software version (skip for WMF-hosted wikis like Wikipedia):

REL1_40

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

This is happened because of T221149.