Zend\InputFilter issue

gistfile1.aw

use Zend\InputFilter\InputFilter,
    Zend\InputFilter\Input;

$input = new Input('foo');
$input->getFilterChain()
      ->attachByName('stringtrim')
      ->attachByName('alpha');

$inputFilter = new InputFilter();
$inputFilter->add($input)
            ->setData(array(
                'foo' => ' Bar3 '
            ));

// if I remove the isValid() the getValue() or getRawValue() return EMPTY values
// $inputFilter->isValid();

echo "Before:\n";
echo $inputFilter->getRawValue('foo') . "\n";
echo "After:\n";
echo $inputFilter->getValue('foo') . "\n";