Unable to prepare route [api/user] for serialization. Uses Closure.

[pitchum]

When running composer install for the first time:

[...]
Package manifest generated successfully.
> Illuminate\Foundation\ComposerScripts::postInstall
> php artisan optimize
Configuration cache cleared!
Configuration cached successfully!
Route cache cleared!

In Route.php line 917:

  Unable to prepare route [api/user] for serialization. Uses Closure.


Script php artisan optimize handling the post-install-cmd event returned with error code 1

Here are the relevant Debian packages I use (from buster repository)

• composer 1.8.4
• php7.3