I just ran into this during do-release-upgrade from 16.04.5 to 18.04.1
as well among other issues. The suggested mv solution worked.
I ended up in a situation where some to-be-upgraded packages like
network-manager-gnome were removed at first but never reinstalled, which
turned out to be
Public bug reported:
zopfli provides a tool/library for PNGs as well as part of its
repository: zopflipng. It'd be great if that tool was made available via
a package just like zopfli itself, since zopflipng is a really useful
tool for web optimizations.
** Affects: zopfli (Ubuntu)
