If the problem is with the index as the staging area for commits (i.e. .git/index), you can simply remove the index (make a backup copy if you want), and then restore index to version in the last commit:
rm -f .git/index
git reset
git add .
git commit -m "git fix message here"
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If that not work, can try this second method.
How? Go to <YOUR_PROJECT_FOLDER>\.git\refs\heads\ and delete the problematic branch from the directory.
Delete .git\refs\heads\<YOUR_BRANCH_NAME>
Followed by reset and commit the files, as showed in the following commands
git reset
git add .
git commit -m "git fix message here"
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The issue of " You are on a branch yet to be born " can be fixed with second method too.
