@sgiehl does this mean the user changed http.blocklist.hosts as it wouldn't be expected otherwise such a notice? I wonder if in that case we would rather need to throw an exception regarding a misconfiguration?

That shouldn't be the problem in that case. The parsed url (where a request should be sent to) doesn't contain a host. This could have various reasons I guess. e.g. a request to file:///tmp/file, is actually valid, but won't contain a host. Not sure what url was requested in that case.