diff --git a/src/main/python/ddadevops/domain/release.py b/src/main/python/ddadevops/domain/release.py
index a639bd5..67da3ef 100644
--- a/src/main/python/ddadevops/domain/release.py
+++ b/src/main/python/ddadevops/domain/release.py
@@ -1,4 +1,5 @@
 from enum import Enum
+from typing import Optional
 from pathlib import Path
 from .common import (
     filter_none,
@@ -21,8 +22,8 @@ class Version():
     def __init__(self, id: Path, version_list: list):
         self.id = id
         self.version_list = version_list
-        self.version_string = None
-        self.is_snapshot = None
+        self.version_string: Optional[str | None] = None
+        self.is_snapshot: Optional[bool | None] = None
 
     def increment(self, release_type: ReleaseType):
         self.is_snapshot = False
@@ -68,8 +69,8 @@ class ReleaseConfig(Validateable):
         main_branch: str,
         config_file: str,
         devops: Devops,
-        release_version: str = None, 
-        bump_version: str = None
+        release_version: Optional[str | None] = None, 
+        bump_version: Optional[str | None] = None
     ):
         self.main_branch = main_branch
         self.config_file = config_file
@@ -78,7 +79,7 @@ class ReleaseConfig(Validateable):
         self.devops = devops
 
 class Release():
-    def __init__(self, release_type: ReleaseType, version: Version, current_branch: str):
+    def __init__(self, release_type: ReleaseType | None, version: Version, current_branch: str):
         self.release_type = release_type
         self.version = version
         self.current_branch = current_branch