UniqueEntityValidator with multiple constraints fails if the first constraint is null

Q	A
Bug report?	yes
Feature request?	no
BC Break report?	no
RFC?	no
Symfony version	2.8.17

Scenario: I'm validating an entity like this

$validator->validate($device, [
    new UniqueEntity([
        'fields' => ['accountId', 'tenantUuid'],
        'em' => $provisioningEm
    ])
]);

If accountId happens to be null, UniqueEntityValidator will now exclude it from the constraint list (since commit 1e3421d ), failing later on because $criteria[$fields[0]] is an invalid array access: fields[0] is the string "accountId", which is not in $criteria.
Reverting lines 88-94 to the version before the commit linked above fixes the issue.

[xabbuh]

@gigib82 Sorry for breaking this. Can you confirm that #21562 fixes the issue for you?

Tested #21562: there is now a behavioural difference with respect to the previous released version.
Using my own example, a null accountId and a non-null tenantUuid used to always pass validation, even if in the DB there was already a record with null accountId and the same tenantUuid. The same scenario now fails validation.
I'm not sure which is the most correct behaviour, but merging this will cause a small BC break.

[xabbuh]

@gigib82 Did you enable or disable the ignoreNull option?

No, never explicitly set that option.

[xabbuh]

@gigib82 You are right. It's not related to the changes from #21562, but was introduced in #21431. You were just not able to see the wrong behaviour due to the initial issue here. I'll work on fixing it completely.

[xabbuh]

@gigib82 I updated #21562. Would you mind checking it again?

The same test suite that spotted the errors is now ok, so I would say #21562 fixes the error

[xabbuh]

Thanks for the confirmation.