diff --git a/swh/model/model.py b/swh/model/model.py
index ee994cdf3eb7b78ad3235541201b73f8cf43acf3..3ee19a83a89e5af67ef7a5a030abc76343ede1ee 100644
--- a/swh/model/model.py
+++ b/swh/model/model.py
@@ -238,6 +238,8 @@ class Release(BaseModel):
         rel = attr.asdict(self)
         rel['date'] = self.date.to_dict() if self.date is not None else None
         rel['target_type'] = rel['target_type'].value
+        if rel['metadata'] is None:
+            del rel['metadata']
         return rel
 
     @classmethod