[UX] Can't use "Fixup" in interactive rebase if parent is the first/ "initial commit"

[ameaninglessname]

I have two commits in the repository, and I want to combine them into one.

When I open up "interactive rebase", "squash" has to be used and has to provide the commit message for the new "first commit".

[ameaninglessname]

When I have 5 commits, I want to combine the first and the second commit.

When using the built-in interactive rebase, choosing squash or fixup, I got the error :

error: cannot 'squash' without a previous commit

git rebase -i --root solved the problem for me.