(*Worktree).Commit will panic if CommitOptions parameter is nil.

[onee-only]

I found that (*Worktree).Commit method is taking pointer as parameter, and derenferencing it without checking if it is nil.
If someone passes nil there, It should panic for sure.

I think if we need users to pass non-nil pointer, we should document it.
Or we could just replace it with pointer to empty struct if it is nil.

I thought about changing the parameter to non-pointer struct, but it seems like it is breaking change and we will lose consistency in codebase.

Example code:

package main

import (
	"github.com/go-git/go-billy/v5/memfs"
	"github.com/go-git/go-billy/v5/util"
	"github.com/go-git/go-git/v5"
	"github.com/go-git/go-git/v5/storage/memory"
)

func main() {
	fs := memfs.New()
	storage := memory.NewStorage()

	r, _ := git.Init(storage, fs)
	w, _ := r.Worktree()

	util.WriteFile(fs, "foo", []byte("foo"), 0755)
	w.Add("foo")

	_, err := w.Commit("this will panic", nil)
	if err != nil {
		panic(err)
	}
}

[onee-only]

Seems like a number of functions in this codebase taking pointer to XXXOptions struct do not check if it is nil.