diff --git a/collections/sentinel-1-global-coherence/create_coherence_items.py b/collections/sentinel-1-global-coherence/create_coherence_items.py
index 85eaf97..ad96d80 100644
--- a/collections/sentinel-1-global-coherence/create_coherence_items.py
+++ b/collections/sentinel-1-global-coherence/create_coherence_items.py
@@ -3,6 +3,7 @@
 from dataclasses import dataclass
 from datetime import datetime, timezone
 from pathlib import Path, PurePath
+from typing import Optional
 
 import boto3
 from shapely import geometry
@@ -57,7 +58,7 @@ class ItemMetadata:
     bbox: geometry.Polygon
     tile: str
     product: str
-    extra: ExtraItemMetadata = None
+    extra: Optional[ExtraItemMetadata] = None
 
 
 def get_s3_url() -> str:
diff --git a/pyproject.toml b/pyproject.toml
index 3d0c04e..21082b1 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -41,3 +41,4 @@ warn_unused_ignores = true
 warn_unreachable = true
 strict_equality = true
 check_untyped_defs = true
+exclude = ["/build/"]