Validation problem with rule MIME_TYPE

[Marian-Kechlibar]

Version: 3.1.11

Bug Description

I need to verify whether a file upload MIME type is actually one of a list of types. The resulting error message is unhelpful.

Steps To Reproduce

addRule($form::MIME_TYPE, $form->getTranslator()->translate('kraken.error.filemustbeoftypewithvalue', array('type' => AlgorithmsAndTypes::TYPE_TEXT_PLAIN)),
                array(AlgorithmsAndTypes::TYPE_TEXT_PLAIN, AlgorithmsAndTypes::TYPE_PEM_ENCODED_FILE , AlgorithmsAndTypes::TYPE_X509_USER_CERT))

where kraken.error.filemustbeoftypewithvalue is defined in NEON translation file as

'Nepodporovaný typ souboru %value.'

The resulting error message is

Nepodporovaný typ souboru [object FileList].

Which does not tell me what MIME type was actually detected by the validator.

Expected Behavior

I would expect an error message that told me exactly what MIME type was detected:

Nepodporovaný typ souboru text/html.

etc.