As pointed out by brian-murray in Bug #987026 cups-pdf is obsoleted in DistUpgrade.cfg https://bugs.launchpad.net/ubuntu/+source/ubuntu-release-upgrader/+bug/987026/comments/7
As pointed out by brian-murray in Bug #987026 cups-pdf is obsoleted in DistUpgrade.cfg /bugs.launchpad .net/ubuntu/ +source/ ubuntu- release- upgrader/ +bug/987026/ comments/ 7
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