[php-src] Issue #8520: Array key evaluation on a null type

Issue: https://github.com/php/php-src/issues/8520 Author: mytuny ### Description When trying to retrieve an array item on a null variable using the syntax null['key'], the key evaluation mechanism still considered. Although this seem to be trivial, such behavior is not expected when used in conjunction with the null-coalescing operator ??. Let's consider the following code: ```php <?php var_dump(null['key'] ?? 'default'); ``` Resulted in this output: ``` default ``` Up to here nothing is clear about whether key evaluation got fired or not. To determine that, we can delegate the key value evaluation to a dynamic function and, also, let's throw an exception from within it to emphasize the behavior clearly: ```php <?php function evalKey() {throw new Exception();} var_dump(null[evalKey()] ?? 'default'); ``` Now, in the context of using the null-coalescing operator one can expect this to lead to the right-hand-side of the operator being outputted without concerns about key evaluation since the evaluated array of the left-hand-side is null at the first place and that's by definition the role of the ?? operator (to test against null & non-existent values)! However, in this scenario the exception is ultimately thrown, which mean that the key is still being evaluated even when the array is null: ``` Fatal error: Uncaught Exception ... ``` Now, it seem we have a competing concerns between array's key evaluation and null coalescing evaluation which lead to some confusing about the expected behavior in such case!! ### PHP Version PHP 8.1.0 ### Operating System _No response_