TypeError when loading ESM scripts from jsdelivr.com

Reduced Test Case

https://jsfiddle.net/tacman1123/917t4mas/2/

Symfony's new AssetMapper component allows loading javascript as easily as loading php files using composer.

However, just like composer loads from packagist.org, importmap loads from jsdelivr.

bin/console importmap:require fullcalendar -vv

10:53:33 INFO      [http_client] Request: "GET https://data.jsdelivr.com/v1/packages/npm/fullcalendar/resolved?specifier=%2A"
10:53:34 INFO      [http_client] Response: "200 https://data.jsdelivr.com/v1/packages/npm/fullcalendar/resolved?specifier=%2A"
10:53:34 INFO      [http_client] Request: "GET https://cdn.jsdelivr.net/npm/[email protected]/+esm"
10:53:34 INFO      [http_client] Request: "GET https://data.jsdelivr.com/v1/packages/npm/[email protected]/entrypoints"
10:53:34 INFO      [http_client] Response: "200 https://cdn.jsdelivr.net/npm/[email protected]/+esm"
10:53:34 INFO      [http_client] Response: "200 https://data.jsdelivr.com/v1/packages/npm/[email protected]/entrypoints"

And as discussed in #7472 , right now the fullcalendar module doesn't load from jsdelivr, only from skypack, which is unmaintained.