Upgrade corrupted due to "sh: 1: pager: not found"

Description: Ubuntu 20.04 LTS
Release: 20.04

dpkg:
  Installed: 1.19.7ubuntu3
  Candidate: 1.19.7ubuntu3
  Version table:
 *** 1.19.7ubuntu3 500
        500 http://us.archive.ubuntu.com/ubuntu focal/main amd64 Packages
        100 /var/lib/dpkg/status

This past weekend I performed an upgrade of Ubuntu 18.04 LTS to Ubuntu 20.04 LTS. I fully updated my 18.04 system and rebooted, then I ran do-release-upgrade -d to start the upgrade.

During the upgrade process for the mime-support package it asked me about changes to /etc/mime.types file:

Configuration file '/etc/mime.types'
 ==> Modified (by you or by a script) since installation.
 ==> Package distributor has shipped an updated version.
   What would you like to do about it ? Your options are:
    Y or I : install the package maintainer's version
    N or O : keep your currently-installed version
      D : show the differences between the versions
      Z : start a shell to examine the situation
 The default action is to keep your current version.
*** mime.types (Y/I/N/O/D/Z) [default=N] ?

I wanted to see the difference so I typed "d" here. Then I got this error:

*** mime.types (Y/I/N/O/D/Z) [default=N] ? d
sh: 1: pager: not found
diff: standard output: Broken pipe
dpkg: error processing package mime-support (--configure):
 conffile difference visualizer subprocess returned error exit status 127

After this, many, MANY packages were failing because mime-support was not configured:

dpkg: dependency problems prevent configuration of python2.7:
 python2.7 depends on mime-support; however:
  Package mime-support is not configured yet.

dpkg: error processing package python2.7 (--configure):
 dependency problems - leaving unconfigured

etc. etc. Eventually it just bailed:

dpkg: too many errors, stopping
Errors were encountered while processing:
 mime-support
 python2.7
   ...
Processing was halted because there were too many errors.

Now my system is in a weird state where it is upgraded and mostly works but I'm missing a bunch of icons, I can't seem to properly select different "Appearance" values from the Settings dialog, etc. I've tried to run "apt dist-upgrade" and "dpkg --configure -a" and neither of those has any impact: they both had no work to do.

I think that breaking the entire install is an overreaction to not being able to run a pager to display a diff: dpkg should handle this error much better and simply say that diffs are not available at this time, but not fail the package configuration!

Of course it would be good to know why "pager" was not available at this point in the upgrade, as well.