ResolveRevision() will panic on empty input string

[abrander]

To reproduce after a simple $ git init .:

package main

import (
	"github.com/go-git/go-git/v5"
	"github.com/go-git/go-git/v5/plumbing"
)

func main() {
	repo, _ := git.PlainOpen(".")
	repo.ResolveRevision(plumbing.Revision(""))
}

I have investigated how to solve this, but I'm unsure if the parser should return an error, or ResolveRevision() should catch the empty items slice. Oh well. Here's the problem:

func (r *Repository) ResolveRevision(rev plumbing.Revision) (*plumbing.Hash, error) {
	p := revision.NewParserFromString(string(rev))

	items, err := p.Parse()

	if err != nil {
		return nil, err
	}

	var commit *object.Commit // <- nil zero value.

	for _, item := range items {
...
	}

	return &commit.Hash, nil // <- dereferences the nil pointer, if the for-loop is never executed.
}

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[abrander]

I have verified that this issue was resolved by #696. I'll close this issue.

v5.6.1 includes the fix.