Can't upgrade to Ubuntu 20.04

[Leandro A. Siqueira]

Running do-release-upgrade, got the error below:

Traceback (most recent call last):
  File "/tmp/ubuntu-release-upgrader-tnrwjlhy/focal", line 8, in <module>
    sys.exit(main())
  File "/tmp/ubuntu-release-upgrader-tnrwjlhy/DistUpgrade/DistUpgradeMain.py", line 238, in main
    if app.run():
  File "/tmp/ubuntu-release-upgrader-tnrwjlhy/DistUpgrade/DistUpgradeController.py", line 2089, in run
    return self.fullUpgrade()
  File "/tmp/ubuntu-release-upgrader-tnrwjlhy/DistUpgrade/DistUpgradeController.py", line 1860, in fullUpgrade
    if not self.prepare():
  File "/tmp/ubuntu-release-upgrader-tnrwjlhy/DistUpgrade/DistUpgradeController.py", line 431, in prepare
    self.openCache()
  File "/tmp/ubuntu-release-upgrader-tnrwjlhy/DistUpgrade/DistUpgradeController.py", line 214, in openCache
    return self._openCache(lock)
  File "/tmp/ubuntu-release-upgrader-tnrwjlhy/DistUpgrade/DistUpgradeController.py", line 242, in _openCache
    lock)
  File "/tmp/ubuntu-release-upgrader-tnrwjlhy/DistUpgrade/DistUpgradeCache.py", line 144, in __init__
    self.linux_metapackage = self.quirks._get_linux_metapackage(self, False)
  File "/tmp/ubuntu-release-upgrader-tnrwjlhy/DistUpgrade/DistUpgradeQuirks.py", line 845, in _get_linux_metapackage
    source = pkg.candidate.record['Source']
AttributeError: 'NoneType' object has no attribute 'record'
Error in sys.excepthook:
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/problem_report.py", line 497, in add_to_existing
    self.write(f)
  File "/usr/lib/python3/dist-packages/problem_report.py", line 450, in write
    block = f.read(1048576)
  File "/usr/lib/python3.6/codecs.py", line 321, in decode
    (result, consumed) = self._buffer_decode(data, self.errors, final)
UnicodeDecodeError: 'utf-8' codec can't decode byte 0x8b in position 1: invalid start byte

Original exception was:
Traceback (most recent call last):
  File "/tmp/ubuntu-release-upgrader-tnrwjlhy/focal", line 8, in <module>
    sys.exit(main())
  File "/tmp/ubuntu-release-upgrader-tnrwjlhy/DistUpgrade/DistUpgradeMain.py", line 238, in main
    if app.run():
  File "/tmp/ubuntu-release-upgrader-tnrwjlhy/DistUpgrade/DistUpgradeController.py", line 2089, in run
    return self.fullUpgrade()
  File "/tmp/ubuntu-release-upgrader-tnrwjlhy/DistUpgrade/DistUpgradeController.py", line 1860, in fullUpgrade
    if not self.prepare():
  File "/tmp/ubuntu-release-upgrader-tnrwjlhy/DistUpgrade/DistUpgradeController.py", line 431, in prepare
    self.openCache()
  File "/tmp/ubuntu-release-upgrader-tnrwjlhy/DistUpgrade/DistUpgradeController.py", line 214, in openCache
    return self._openCache(lock)
  File "/tmp/ubuntu-release-upgrader-tnrwjlhy/DistUpgrade/DistUpgradeController.py", line 242, in _openCache
    lock)
  File "/tmp/ubuntu-release-upgrader-tnrwjlhy/DistUpgrade/DistUpgradeCache.py", line 144, in __init__
    self.linux_metapackage = self.quirks._get_linux_metapackage(self, False)
  File "/tmp/ubuntu-release-upgrader-tnrwjlhy/DistUpgrade/DistUpgradeQuirks.py", line 845, in _get_linux_metapackage
    source = pkg.candidate.record['Source']
AttributeError: 'NoneType' object has no attribute 'record'

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubuntu-release-upgrader-core 1:18.04.42
ProcVersionSignature: Ubuntu 5.4.0-42.46~18.04.1-generic 5.4.44
Uname: Linux 5.4.0-42-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.23
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: Unity
Date: Mon Mar 8 19:22:02 2021
InstallationDate: Installed on 2021-03-05 (3 days ago)
InstallationMedia: Ubuntu 18.04.5 LTS "Bionic Beaver" - Release amd64 (20200806.1)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
Symptom: ubuntu-release-upgrader
UpgradeStatus: Upgraded to bionic on 2021-03-08 (0 days ago)
mtime.conffile..etc.update-manager.release-upgrades: 2021-03-06T11:59:59.599761

[Julian Andres Klode (juliank)]

Your pinning is causing this issue:

Package: linux-image*
Pin: release n=bionic
Pin-Priority: -1

Because if you upgrade to bionic, you prevented it from installing any kernels!