framework/validators/FileValidator.php
public function isEmpty($value, $trim = false)
    {
        $value = is_array($value) ? reset($value) : $value;
        return !($value instanceof UploadedFile) || $value->error == UPLOAD_ERR_NO_FILE;
    }
public function isEmpty($value, $trim = false)
    {
        $value = is_array($value) ? reset($value) : $value;
        return !($value instanceof UploadedFile) || $value->error == UPLOAD_ERR_NO_FILE;
    }
{@inheritdoc}
@param bool $trim