public function getInclude(array $available = [])
    {
        if ($include = $this->getInput('include')) {
            $relationships = explode(',', $include);

            $invalid = array_diff($relationships, $available);

            if (count($invalid)) {
                throw new InvalidParameterException(
                    'Invalid includes ['.implode(',', $invalid).']',
                    1,
                    null,
                    'include'
                );
            }

            return $relationships;
        }

        return [];
    }