Skip "parentsigned" check when the repo is empty (#35292)

Fix #35280

services/asymkey/sign.go

@@ -290,6 +290,11 @@ Loop:
 				return false, nil, nil, err
 			}
 			defer gitRepo.Close()
+			isEmpty, err := gitRepo.IsEmpty()
+			if err != nil {
+				return false, nil, nil, err
+			}
+			if !isEmpty {
 				commit, err := gitRepo.GetCommit(parentCommit)
 				if err != nil {
 					return false, nil, nil, err
@@ -303,6 +308,7 @@ Loop:
 				}
 			}
 		}
+	}
 	return true, signingKey, sig, nil
 }