diff --git a/tiddl/models/resource.py b/tiddl/models/resource.py
index 277fc03..0be90d0 100644
--- a/tiddl/models/resource.py
+++ b/tiddl/models/resource.py
@@ -120,7 +120,7 @@ class Album(BaseModel):
     numberOfTracks: int
     numberOfVideos: int
     numberOfVolumes: int
-    releaseDate: str
+    releaseDate: Optional[str] = None
     copyright: Optional[str] = None
     type: str
     version: Optional[str] = None