Why am I getting Undefined property: stdClass:: with php 8 nullsafe operator

Php 8.0 introduced the nullsafe operator which can be used like so $foo?->bar?->baz;.
I have a code sample running on php 8.1 that throws the error Undefined property: stdClass::$first_name even though it is using the nullsafe operator:

$reference = (object) $reference; // Cast of array to object

return [
    'FirstName' => $reference?->first_name,
];

To solve the error, I have to use the null coalescing operator:

$reference = (object) $reference; // Cast of array to object

return [
    'FirstName' => $reference->first_name ?? null,
];

Why is the nullsafe operator throwing an error in this case?

>Solution :

You seem to have a slight misunderstanding of what the nullsafe operator does.

If $reference was null, then $reference?->first_name would return null with no warning, but since $reference is actually an object, ?-> just functions like a normal object operator, hence the undefined property warning.