diff --git a/lib/galaxy/model/metadata.py b/lib/galaxy/model/metadata.py
index bff4109560f..97fe0df49be 100644
--- a/lib/galaxy/model/metadata.py
+++ b/lib/galaxy/model/metadata.py
@@ -113,6 +113,7 @@ class MetadataCollection(Mapping):
             return self.spec[name].wrap(self.spec[name].default, object_session(self.parent))
         if name in self.parent._metadata:
             return self.parent._metadata[name]
+        # Instead of raising an AttributeError for non-existing metadata, we return None
         return None
 
     def __setattr__(self, name, value):