[TypeError] ArrayIterator::__construct(): Argument #1 ($array) must be of type array, null given

[fritzmg]

This error happens during cache:warmup:

[TypeError]
    ArrayIterator::__construct(): Argument #1 ($array) must be of type array, null given  

                                                                                                                                                                                                              
  Exception trace:
    at vendor\netzmacht\contao-leaflet-maps\src\Frontend\Assets\LibrariesConfiguration.php:54
   ArrayIterator->__construct() at vendor\netzmacht\contao-leaflet-maps\src\Frontend\Assets\LibrariesConfiguration.php:54
   Netzmacht\Contao\Leaflet\Frontend\Assets\LibrariesConfiguration->getIterator() at vendor\netzmacht\contao-leaflet-maps\src\Listener\RegisterLibrariesListener.php:61       
   Netzmacht\Contao\Leaflet\Listener\RegisterLibrariesListener->onInitializeSystem() at vendor\contao\core-bundle\src\Framework\ContaoFramework.php:405
   Contao\CoreBundle\Framework\ContaoFramework->triggerInitializeSystemHook() at vendor\contao\core-bundle\src\Framework\ContaoFramework.php:307
   Contao\CoreBundle\Framework\ContaoFramework->initializeFramework() at vendor\contao\core-bundle\src\Framework\ContaoFramework.php:122
   Contao\CoreBundle\Framework\ContaoFramework->initialize() at vendor\contao\core-bundle\src\Cache\ContaoCacheWarmer.php:62
   Contao\CoreBundle\Cache\ContaoCacheWarmer->warmUp() at vendor\symfony\http-kernel\CacheWarmer\CacheWarmerAggregate.php:99
   Symfony\Component\HttpKernel\CacheWarmer\CacheWarmerAggregate->warmUp() at vendor\symfony\framework-bundle\Command\CacheWarmupCommand.php:83
   Symfony\Bundle\FrameworkBundle\Command\CacheWarmupCommand->execute() at vendor\symfony\console\Command\Command.php:298
   Symfony\Component\Console\Command\Command->run() at vendor\symfony\console\Application.php:1058
   Symfony\Component\Console\Application->doRunCommand() at vendor\symfony\framework-bundle\Console\Application.php:96
   Symfony\Bundle\FrameworkBundle\Console\Application->doRunCommand() at vendor\symfony\console\Application.php:301
   Symfony\Component\Console\Application->doRun() at vendor\symfony\framework-bundle\Console\Application.php:82
   Symfony\Bundle\FrameworkBundle\Console\Application->doRun() at vendor\symfony\console\Application.php:171
   Symfony\Component\Console\Application->run() at vendor\contao\manager-bundle\bin\contao-console:38

This is related to #120, #127 and #124

The issue is the initializeSystem Hook RegisterLibrariesListener::onInitializeSystem. This hook will be called early during the cache warmup - and at that point the loading order of the legacy modules does not matter yet. That's why $GLOBALS['LEAFLET_LIBRARIES'] is not populated and thus leads to this error.

[fritzmg]

Ah, this error only occurs if you have a mis-configured composer.json ("type": "project" was missing - which then will not install any Contao 2/3 style extensions).