This got updated recently in 42a42c96acc5193dbb6e321ff2aaecceb00e48a4
to split out the livecheck audits and as a result of that the type
signature for the #validate_url_for_https_availablity method got updated.
This did not account for the possibility that the livecheck url was nil.
I've added a nil check here since it makes no sense to try and validate
a nil url and we have nil checks for the other two http availability
audits already. Plus, the livecheck blocks are audited thoroughly already
for syntax.
926c5b739a