Here https://lists.ubuntu.com/archives/ubuntu- devel/2020-October/041237.html is a suggestion to sync from Groovy to Focal in order to fix the issue:
> I checked Calibre in Groovy (version 4.99.12+dfsg+really4.23.0-1) and it works fine. As per bug report #1898904 (https://bugs.launchpad.net/ubuntu/+source/calibre/+bug/1898904/comments/7), Calibre >=4.15 has the required patch. So, instead of waiting for 5.2, can we backport current Groovy version of Calibre to Focal? -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1898904 Title: Calibre crashes at startup with AttributeError: 'NoneType' object has no attribute 'cancel' To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/calibre/+bug/1898904/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
