public function areReturnTypesCompatible()
    {
        // null | T1 | T2
        if (\count($this->returnTypes) > 2) {
            return false;
        }

        // T1 | T2
        if (2 == \count($this->returnTypes) && !isset($this->returnTypes['null'])) {
            return false;
        }

        return true;
    }