fix: throw error when trying to backport single undefined commit

[lampajr]

Thank you for submitting this pull request

fixes #176

Description

Since, by default, squash is set to true (when omitted).. if the process tries to backport a single squashed/merged commit from a merged PR/MR and the commit is undefined (e.g., in the case of fast-forward merge in Gitlab), the process should immediately abort with an error.

The solution in that case is to either set --auto-no-squash or explicitly disable squash with --no-squash which will make the process trying to merge all the original commits.

How Has This Been Tested?

Added new test case for the new behavior

Checklist

• Tests added if applicable.
• Documentation updated if applicable.

Merge criteria:

• The commits and have meaningful messages; the author will squash them after approval or will ask to merge with squash.
• Testing instructions have been added in the PR body (for PRs involving changes that are not immediately obvious).
• The developer has manually tested the changes and verified that the changes work

Note: dist/cli/index.js and dist/gha/index.js are automatically generated by git hooks and gh workflows.

First time here?

This project follows git conventional commits pattern, therefore the commits should have the following format:

<type>(<optional scope>): <subject>
empty separator line
<optional body>
empty separator line
<optional footer>

Where the type must be one of [build, chore, ci, docs, feat, fix, perf, refactor, revert, style, test]

NOTE: if you are still in a work in progress branch and you want to push your changes remotely, consider adding --no-verify for both commit and push, e.g., git push origin <feat-branch> --no-verify - this could become useful to push changes where there are still tests failures. Once the pull request is ready, please amend the commit and force-push it to keep following the adopted git commit standard.

How to prepare for a new release?

There is no need to manually update package.json version and CHANGELOG.md information. This process has been automated in Prepare Release Github workflow.

Therefore whenever enough changes are merged into the main branch, one of the maintainers will trigger this workflow that will automatically update version and changelog based on the commits on the git tree.

More details can be found in package release section of the README.

[github-actions]

Coverage report

St.❔	Category	Percentage	Covered / Total
🟢	Statements	89.37% (+0.17% 🔼)	513/574
🟢	Branches	85.42% (-0.04% 🔻)	246/288
🟢	Functions	87.6% (+0.1% 🔼)	113/129
🟢	Lines	89.21% (+0.16% 🔼)	496/556

Show files with reduced coverage 🔻

St.❔	File	Statements	Branches	Functions	Lines
🟢	... / pr-configs-parser.ts	98.39% (+1.78% 🔼)	96.88% (-1.51% 🔻)	100%	98.33% (+1.78% 🔼)
🟢	... / github-mapper.ts	82.35% (-3.36% 🔻)	70.83% (-1.89% 🔻)	80%	86.67% (-5% 🔻)

Test suite run success

218 tests passing in 18 suites.

Report generated by 🧪jest coverage report action from 7abdf64