problem with form validation

[michalbundyra]

I use a form to validate the input of my json rest api, but an exception occurs when i get a value that is not an array for a fieldset. Here an example:

All fine:
{
"article": {
"id": 1
}
}

All fine:
{
}

Exception in inputfilter
{
"article": null
}

Validationgroup is array("article" => array("id"))

How to allow article to be anything and get a validation error if its not an array with a valid id?

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Originally posted by @sneps85 at zendframework/zend-form#44