Heads up: PHP 7.4 breaking changes

[Devristo]

Note: this issue is just a heads up. I know PHP 7.4 might be out of your scope for now. But there are some 'breaking changes' to watch out for.

For example due to php/php-src#4386 the following line will throw an error when $parentOperation is null:

core/src/Operation/Factory/SubresourceOperationFactory.php

Line 78 in 345612c

$isLastItem = $resourceClass === $parentOperation['resource_class'] && $propertyMetadata->isIdentifier();

Possibly running the tests on PHP 7.4 would uncover more issues.

[teohhanhui]

See #3036

[Devristo]

Perfect ! 🎉