When try to upgrade a Plesk license in CP an Application Error occures. The following could be found in
Error-TEXT: 54:33] [FATAL]  [HSPC::Site::Layout::build_content] Can't call method "ka_key" on an undefined value at /usr/local/share/perl5/HSPC/Plugin/LM/KA.pm line 2099. ERROR : no result from component,cmd=$res=HSPC::CP::Upgrade->teaser_start(_component_id=>10376); Error-LOCATION: /usr/local/share/perl5/HSPC/Logger.pm:161
Such behavior was classified as the software issue PBAS-30168. It was fixed in OBAS 4.5.6
To resolve the issue, please upgrade to 4.5.6 as described in How to upgrade OBAS system to the latest available version.