Safari: "Manifest content_scripts section has no specified matches entry."

I just tried building the WebExtension version of NoScript as a Safari Web Extension. After allowing unsigned extensions and running the app, the extension appears in Safari. However, an error message is displayed:

Manifest content_scripts section has no specified matches entry.

This is not true. I've tried editing the NoScript manifest.json to replace the "<all_urls>" annotation with something standard like "http://*/*", but that doesn't seem to help.
This is likely due to the match patterns for file and ftp. Safari does not support extensions for those schemes, so the matches array will appear empty after those unsupported patterns are filtered out.
Safari: "Manifest content_scripts section has no specified matches entry."
 
 
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