Utility/Fields/File.php
public function valid()
    {
        $bResult = false;
        if ($this->getOption('required') == 'true') {
            $value = $this->getValue();
            if (empty($value)) {
                $this->isValid = false;
            } else {
                $bResult = true;
            }
        } else {
            $bResult = true;
        }

        return $bResult;
    }
public function valid()
    {
        $bResult = false;
        if ($this->getOption('required') == 'true') {
            $value = $this->getValue();
            if (empty($value)) {
                $this->isValid = false;
            } else {
                $bResult = true;
            }
        } else {
            $bResult = true;
        }

        return $bResult;
    }
Check validator with field.

@return bool