If the property is non-static an object must be provided to fetch the
property from.
Return Values
Returns false for typed properties prior to initialization,
and for properties that have been explicitly unset().
For all other properties true will be returned.
Example #1 ReflectionProperty::isInitialized() example
<?php
class User
{
public string $name;
}
$rp = new ReflectionProperty('User', 'name');
$user = new User;
var_dump($rp->isInitialized($user));
$user->name = 'Nikita';
var_dump($rp->isInitialized($user));
?>