Comment 64 for bug 1990450

Got 18.04.6 ISO and run it in virtual machine.

Updated ubuntu-advange-tools, installed hello package (as it is listed in https://esm.ubuntu.com/apps/ubuntu/dists/jammy-apps-security/main/binary-amd64/Packages), enabled proposed in software-properties-gtk, installed update-manager .20.

Ran update-manager, got error:

--->
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/UpdateManager/backend/InstallBackendAptdaemon.py", line 248, in _on_finished
    trans_failed=trans_failed)
  File "/usr/lib/python3/dist-packages/UpdateManager/backend/__init__.py", line 95, in _action_done
    self.window_main.start_available(is_cancelled_update)
  File "/usr/lib/python3/dist-packages/UpdateManager/UpdateManager.py", line 242, in start_available
    self.refresh_cache()
  File "/usr/lib/python3/dist-packages/UpdateManager/UpdateManager.py", line 441, in refresh_cache
    self._get_ua_security_status()
  File "/usr/lib/python3/dist-packages/UpdateManager/UpdateManager.py", line 264, in _get_ua_security_status
    s = json.load(p.stdout)
  File "/usr/lib/python3.6/json/__init__.py", line 299, in load
    parse_constant=parse_constant, object_pairs_hook=object_pairs_hook, **kw)
  File "/usr/lib/python3.6/json/__init__.py", line 354, in loads
    return _default_decoder.decode(s)
  File "/usr/lib/python3.6/json/decoder.py", line 339, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/usr/lib/python3.6/json/decoder.py", line 357, in raw_decode
    raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)
<---

This was caused by something in ubuntu-advantage-tools update to 29.4~18.04, as it is not reproducible in 29.3~18.04.