Index: pkg/polymer/lib/src/instance.dart |
diff --git a/pkg/polymer/lib/src/instance.dart b/pkg/polymer/lib/src/instance.dart |
index f0bff99c4637274b00dd6c5d15419547f71b76d9..67f577b6a8ae966b4489886376cfa0a9d17d421e 100644 |
--- a/pkg/polymer/lib/src/instance.dart |
+++ b/pkg/polymer/lib/src/instance.dart |
@@ -273,7 +273,7 @@ class PolymerElement extends CustomElement with ObservableMixin { |
void copyInstanceAttributes() { |
_declaration._instanceAttributes.forEach((name, value) { |
- attributes[name] = value; |
+ attributes.putIfAbsent(name, () => value); |
}); |
} |