Currently the null-safe operator in the expression language doesn't behave the same as in PHP. According to the RFC:

When the evaluation of one element in the chain fails the execution of the entire chain is aborted and the entire chain evaluates to null.

For example, in PHP the following expressions will return null:

$foo = null;
$foo?->bar['baz'];
$foo?->bar['baz']['qux'];
$foo?->bar['baz']['qux']->quux;
$foo?->bar['baz']['qux']->quux();

This, however, is not the case with the null-safe operator in the expression language where the evaluation for such cases fails.

Not sure if this qualifies as a bug fix or a feature, so please let me know.