Bug#1120448: apt modernize-sources swallows problem

Package: apt
Version: 3.1.11

# apt modernize-sources
The following files need modernizing:
  - /etc/apt/sources.list.d/google-chrome-beta.list
  - /etc/apt/sources.list.d/google-earth-pro.list

Modernizing will replace .list files with the new .sources format,
add Signed-By values where they can be determined automatically,
and save the old files into .list.bak files.

This command supports the 'signed-by' and 'trusted' options. If you
have specified other options inside [] brackets, please transfer them
manually to the output files; see sources.list(5) for a mapping.

For a simulation, respond N in the following prompt.
Rewrite 2 sources? [Y/n] 
Modernizing /etc/apt/sources.list.d/google-chrome-beta.list...
- Writing /etc/apt/sources.list.d/google-chrome-beta.sources

Modernizing /etc/apt/sources.list.d/google-earth-pro.list...
- Writing /etc/apt/sources.list.d/google-earth-pro.sources
Warning: Could not determine Signed-By for URIs: http://dl.google.com/linux/earth/deb/, Suites: stable

# apt modernize-sources
All sources are modern.

At this point the user thinks "what about that problem? I guess all is
well and good now." (Only to still get errors on apt update.)

So at least more should be output, not just "All sources are modern."