try with branch reference name

utils/git.go

@@ -215,7 +215,7 @@ func (gm *GitManager) CheckoutToHash(hash string) error {
 
 func (gm *GitManager) GetBestCommonAncestorHash(baseBranch, headBranch string) (string, error) {
 	// Get the commit object of the base branch
-	baseRef, err := gm.localGitRepository.Reference(GetFullBranchName(baseBranch), true)
+	baseRef, err := gm.localGitRepository.Reference(plumbing.NewBranchReferenceName(baseBranch), true)
 	if err != nil {
 		return "", err
 	}
@@ -224,8 +224,13 @@ func (gm *GitManager) GetBestCommonAncestorHash(baseBranch, headBranch string) (
 		return "", err
 	}
 	log.Debug(fmt.Sprintf("Found commit %s for base branch %s", baseCommit.Hash.String(), baseBranch))
-	// Get the commit object of the head branch
-	headRef, err := gm.localGitRepository.Reference(GetFullBranchName(headBranch), true)
+	// Get the commit object of the head branch (can have no references, initial commit...)
+	// headRef, err := gm.localGitRepository.Reference(GetFullBranchName(headBranch), true)
+	// if err != nil {
+	// 	return "", err
+	// }
+
+	headRef, err := gm.localGitRepository.Reference(plumbing.NewBranchReferenceName(headBranch), true)
 	if err != nil {
 		return "", err
 	}