Setting yubikey verification URL to an empty value does not fallback to Yubikey_Webclient URL
- Set yubikey2fUrl to ""
- Try to use yubikey
- fails because the lib defines the verification URL to an empty string instead of falling back to default
A user can fall into this case when putting in a custom Yubikey verification URL (for testing) and then replacing it with an empty string
[debug] Reading Yubikey ... Use of uninitialized value in scalar chomp at /usr/local/share/perl5/Auth/Yubikey_WebClient.pm line 210. Use of uninitialized value in pattern match (m//) at /usr/local/share/perl5/Auth/Yubikey_WebClient.pm line 212. Use of uninitialized value in pattern match (m//) at /usr/local/share/perl5/Auth/Yubikey_WebClient.pm line 214. Use of uninitialized value $1 in concatenation (.) or string at /usr/local/share/perl5/Auth/Yubikey_WebClient.pm line 215. [warn] Yubikey verification failed