ZF2 non required input filter

gistfile1.txt

<?php
namespace Application\InputFilter;

use Zend\InputFilter as ZFI;

class InputFilter extends ZFI\InputFilter
{
    private $required = true;

    /**
     * @return boolean
     */
    public function isRequired()
    {
        return $this->required;
    }

    /**
     * @param boolean $required
     *
     * @return $this
     */
    public function setRequired($required)
    {
        $this->required = (bool) $required;
        return $this;
    }

    /**
     * @return bool
     */
    public function isValid()
    {
        if (!$this->isRequired() && empty(array_filter($this->getRawValues()))) {
            return true;
        }

        return parent::isValid();
    }
}