fix(gitutil): don't crash if no last version was found

internal/gitutil/gitutil.go

@@ -123,10 +123,19 @@ func (g *GitUtil) GetLastVersion() (*semver.Version, *plumbing.Reference, error)
 // GetCommits from git hash to HEAD
 func (g *GitUtil) GetCommits(lastTagHash *plumbing.Reference) ([]shared.Commit, error) {
 
-	excludeIter, err := g.Repository.Log(&git.LogOptions{From: lastTagHash.Hash()})
+	ref, err := g.Repository.Head()
 	if err != nil {
 		return nil, err
 	}
+	logOptions := &git.LogOptions{From: ref.Hash()}
+
+	if lastTagHash != nil {
+		logOptions = &git.LogOptions{From: lastTagHash.Hash()}
+	}
+	excludeIter, err := g.Repository.Log(logOptions)
+	if err != nil {
+		return nil, fmt.Errorf("could not get git log %w", err)
+	}
 
 	seen := map[plumbing.Hash]struct{}{}
 	err = excludeIter.ForEach(func(c *object.Commit) error {
@@ -142,10 +151,6 @@ func (g *GitUtil) GetCommits(lastTagHash *plumbing.Reference) ([]shared.Commit,
 		return !ok && len(commit.ParentHashes) < 2
 	}
 
-	ref, err := g.Repository.Head()
-	if err != nil {
-		return nil, err
-	}
 	startCommit, err := g.Repository.CommitObject(ref.Hash())
 	if err != nil {
 		return nil, err

pkg/semanticrelease/semantic-release.go

@@ -1,6 +1,7 @@
 package semanticrelease
 
 import (
+	"fmt"
 	"github.com/Nightapes/go-semantic-release/internal/integrations"
 	"io/ioutil"
 	"time"
@@ -102,7 +103,7 @@ func (s *SemanticRelease) GetNextVersion(provider *ci.ProviderConfig, force bool
 
 	commits, err := s.gitUtil.GetCommits(lastVersionHash)
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("could not get commits %w", err)
 	}
 
 	log.Debugf("Found %d commits till last release", len(commits))
@@ -131,12 +132,15 @@ func (s *SemanticRelease) GetNextVersion(provider *ci.ProviderConfig, force bool
 			Version: &newVersion,
 		},
 		Last: shared.ReleaseVersionEntry{
-			Commit:  lastVersionHash.Hash().String(),
+			Commit:  "",
 			Version: lastVersion,
 		},
 		Branch:  provider.Branch,
 		Commits: analyzedCommits,
 	}
+	if lastVersionHash != nil {
+		releaseVersion.Last.Commit = lastVersionHash.Hash().String()
+	}
 
 	if firstRelease {
 		releaseVersion.Last.Version, _ = semver.NewVersion("0.0.0")