diff --git a/datumaro/datumaro/components/extractor.py b/datumaro/datumaro/components/extractor.py
index 3180665f..ae0c1fae 100644
--- a/datumaro/datumaro/components/extractor.py
+++ b/datumaro/datumaro/components/extractor.py
@@ -378,7 +378,9 @@ class _Shape(Annotation):
             id=None, attributes=None, group=None):
         super().__init__(id=id, type=type,
             attributes=attributes, group=group)
-        self._points = points
+        if points is None:
+            points = []
+        self._points = list(points)
 
         if label is not None:
             label = int(label)