If the bug is confirmed, I have a ready patch.

When you call getValue() does it give an exception in this case? (non-existing key).
https://github.com/symfony/symfony/blob/master/src/Symfony/Component/PropertyAccess/PropertyAccessorInterface.php#L103-L104

@sstok, for $array it gives NULL, for $object it throws an exception saying that no getter/isser/hasser found.

OK, so it's directly confirmable. Hmm..

@sstok It seems that tests expect this behavior. That sounds strange to me, seems that for you too.

After investigation, it's the expected behavior. The second argument of PropertyAccessor::__construct() determines if exceptions should be thrown or not, if it is set to true, isReadable properly returns false.
I'll close this issue, the attached PR #18970 , then open a new PR to allow passing this argument in PropertyAccess::createPropertyAccessor (e.g. createPropertyAccessor($throwExceptionOnInvalidIndex = false)).

May I ask how this was decided? I find it a bit confusing that the exceptions differ from objects and arrays.

There was nothing to change as this is the expected behaviour (accessing non-existing array keys just returns null, see http://symfony.com/doc/current/components/property_access.html#reading-from-arrays).

It can be useful with multidimensional array.

$array = array();
$accessor->isReadable($array, '[foo]'); // true
$accessor->isReadable($array, '[foo][bar]'); // false

Because

$array = array();
$accessor->getValue($array, '[foo]'); // null
$accessor->getValue($array, '[foo][bar]'); // Exception\UnexpectedTypeException - "PropertyAccessor requires a graph of objects or arrays to operate on, but it found type "NULL" while trying to traverse path "[foo][bar]" at property "bar"."