Check if JSON key exists in PHP

$houseNr = $user->address->houseNr ?? 'NA';

In the case of a JSON object if you try to access data with a key that doesn't exist then you will get the following warning:

To avoid this warning you need to test if the key exists or not. In PHP 7 the Null coalescing operator was introduced which makes this process quite simple:

$houseNr = $user->address->houseNr ?? 'NA';