Check on missing Assertion element in Response

Hello.
According to the SPID Quality Assessment Document ( https://www.spid.gov.it/assets/download/SPID_QAD.pdf ), test 3.32,
if the Assertion element is missing, the Service Provider should give an error message.

This lib, perform tests on the assertion:
https://github.com/italia/spid-php-lib/blob/29888e0e43c15b5778d89672990d8167aa880d93/src/Spid/Saml/In/Response.php#L66

but it doesn't throw an exception if the element is not present in the response.
In fact, when performing tests with the spid-testenv2 ( https://github.com/italia/spid-testenv2 ), if i check the "Assertion assente" option. i can't login but i don't get any error message.

Looking at the spid-php-lib code, it seems to be legitimate to have no Assertion, so i don't really know which way to go, whether to add the exception or leave the code as it is.
Could you give me some suggestions? Thank you.