File Validator strange behavior

I am using "Validation\Validator\File" to validate an uploaded file:

    $validator->add(
            'image',
            new Validation\Validator\File([
                'maxSize' => $this->getValidationConfig()->maxSize,
                'allowedTypes' => $this->getValidationConfig()->allowedTypes,
                'maxResolution' => $this->getValidationConfig()->maxResolution,
                'messageSize' => ':field exceeds ' . DigitalUnitsConverterUtil::bytesToMb(
                    $this->getValidationConfig()->maxSize) . ' Mb',
                'allowEmpty' => false
            ])
        );

The value being validated is:

    $validator->validate([
        'image' => $this->image,
    ])

And $this->image is being set inside method "onConstruct()":

    public function onConstruct()
    {
        $this->image = $this->request->getUploadedFiles('image')[0];
    }

But, always the validator says that value is empty. I used xdebug to check, but the value is not empty and contains "Phalcon\Http\Request\File".

What is going wrong ?