Ok, I see the 'App' facade is no longer registered in Laravel\Lumen\Application. Not sure why.
/**
* Register the facades for the application.
*
* @return void
*/
public function withFacades()
{
Facade::setFacadeApplication($this);
if (! static::$aliasesRegistered) {
static::$aliasesRegistered = true;
class_alias('Illuminate\Support\Facades\Auth', 'Auth');
class_alias('Illuminate\Support\Facades\Cache', 'Cache');
class_alias('Illuminate\Support\Facades\DB', 'DB');
class_alias('Illuminate\Support\Facades\Event', 'Event');
class_alias('Illuminate\Support\Facades\Gate', 'Gate');
class_alias('Illuminate\Support\Facades\Log', 'Log');
class_alias('Illuminate\Support\Facades\Queue', 'Queue');
class_alias('Illuminate\Support\Facades\Schema', 'Schema');
class_alias('Illuminate\Support\Facades\Validator', 'Validator');
}
}