autopkgtest task error due to environment lookup failure does not provide useful user feedback

https://debusine.freexian.com/freexian/elts/work-request/8516/ is an autopkgtest workrequest that resulted in an error. No useful user feedback is displayed in the web. The actual failure is visible from the system log.

WorkRequest 8516 failed to pre-process task data, aborting it. Task data: {'input': {'source_artifact': '45837@artifacts', 'binary_artifacts': ['internal@collections/name:build-all'], 'context_artifacts': []}, 'backend': 'incus-lxc', 'fail_on': {}, 'timeout': None, 'debug_level': 0, 'environment': 'freexian/match:codename=buster', 'exclude_tests': [], 'include_tests': [], 'needs_internet': 'run', 'extra_environment': {}, 'host_architecture': 'amd64', 'extra_repositories': [{'url': 'http://deb.freexian.com/extended-lts-staging', 'suite': 'buster-lts-proposed', 'components': ['main', 'contrib', 'non-free']}]} Error: "'freexian' has no item 'match:codename=buster:architecture=amd64:format=tarball:backend=incus-lxc'"