private function extractFilters(array $params)
    {
        if (false === $this->issetNotEmpty(self::PARAM_FILTERING, $params)) {
            return $this;
        }
        $filters = $params[self::PARAM_FILTERING];
        if (!is_array($filters)) {
            throw RestException::invalidQueryParam(self::PARAM_FILTERING, 'The filter parameter must be an array keyed by filter name and value.');
        }
        foreach ($filters as $key => $value) {
            $this->filters[$key] = $value;
        }
        return $this;
    }