Add workaround for YouTube Shorts links (#17869)

* Add workaround for YouTube Shorts links

* Update link_details_extractor_spec.rb

app/lib/link_details_extractor.rb

@@ -208,7 +208,7 @@ class LinkDetailsExtractor
   end
 
   def valid_url_or_nil(str, same_origin_only: false)
-    return if str.blank?
+    return if str.blank? || str == 'null'
 
     url = @original_url + Addressable::URI.parse(str)