Better DX error handling when misuse of SymfonyExtension config

[symfonyaml]

Issue

As a dummy symfony user, when I don't use the MinkExtension correctly with the following config

# behat.yml.dist
...
    extensions:
        Behat\MinkExtension: ~   # <---- empty invalid config

we have the following PHP fatal error :

PHP Fatal error: Uncaught TypeError: array_key_exists():
Argument #2 ($array) must be of type array, null given in MinkExtension.php:120

Reproduce

composer create-project symfony/symfony-demo mink-reproduce-bug
cd ./mink-reproduce-bug
composer require --dev behat/behat friends-of-behat/symfony-extension friends-of-behat/mink-extension
echo "        Behat\MinkExtension: ~" >> behat.yml.dist
vendor/bin/behat

Solution

Checking that the config is an array, so we get this error instead :

[stof]

A better implementation of the fix would be to run the normalization step only for arrays by replacing the always() condition with ifArray().