Steps to replicate the issue

1. Navigate to https://mediawiki.org/wiki/Project:Support_desk?safemode=1.
2. Click the "Add topic" button at the top-right of the page.
3. At the top-right of the box labeled "Description" within the 'new topic' area, click the "Source" button (to switch the box to source-mode).
4. Click the "Link" icon in the toolbar (or press Ctrl/Cmd+K).
5. In the "Add a link" box that appears, click "External site".
6. Paste in/type a link to any external site.
7. Click the "Insert" button at the top-right of the "Add a link" box.

What happens?
The link isn't inserted, the "Add a link" menu doesn't allow me to either insert the link or close the box, and I get the following error in the browser console:

Uncaught TypeError: can't access property "element", this.initialAnnotation is null
    getTeardownProcess ve.ui.MWWikitextLinkAnnotationInspector.js:307

What should have happened instead?:
Link should have been added / editor shouldn't've frozen.

Software version
1.45.0-wmf.18

Other information
Could repro on Chrome + Edge + Firefox. Haven't tried any others.