github-tag-action: v5.1 doesn't generate tags

Dependabot suggested I upgrade from v5 to v5.1 and following the upgrade I get…

2020-11-25T07:30:43.9712609Z ##[group]Run mathieudutour/github-tag-action@v5.1
2020-11-25T07:30:43.9713244Z with:
2020-11-25T07:30:43.9714368Z   github_token: ***
2020-11-25T07:30:43.9714710Z   release_branches: main
2020-11-25T07:30:43.9715050Z   default_bump: patch
2020-11-25T07:30:43.9715367Z   tag_prefix: v
2020-11-25T07:30:43.9715694Z   create_annotated_tag: false
2020-11-25T07:30:43.9716017Z   dry_run: false
2020-11-25T07:30:43.9716311Z ##[endgroup]
2020-11-25T07:30:44.2027246Z ##[group]Run actions/create-release@v1
2020-11-25T07:30:44.2027669Z with:
2020-11-25T07:30:44.2028034Z   release_name: Release 
2020-11-25T07:30:44.2028397Z   draft: false
2020-11-25T07:30:44.2028758Z   prerelease: false
2020-11-25T07:30:44.2029085Z env:
2020-11-25T07:30:44.2029841Z   GITHUB_TOKEN: ***
2020-11-25T07:30:44.2030175Z ##[endgroup]
2020-11-25T07:30:44.2796025Z ##[error]Input required and not supplied: tag_name

when I downgrade to v5 again, it works perfectly. There is no new tag created via v5.1