public function filter($key, $value = null)
    {
        if ($value === null) {
            return $this;
        }

        if (is_array($value)) {
            if (array_key_exists('min', $value)) {
                $this->params['filter'][$key . '_von'] = $value['min'];
            }
            if (array_key_exists('max', $value)) {
                $this->params['filter'][$key . '_bis'] = $value['max'];
            }

            if (array_key_exists('min', $value) || array_key_exists('max', $value)) {
                return $this;
            }
        }

        $this->params['filter'][$key] = $value;

        return $this;
    }