diff --git a/cura/Arranging/ShapeArray.py b/cura/Arranging/ShapeArray.py
index 45454f6239..3060ea6e8e 100644
--- a/cura/Arranging/ShapeArray.py
+++ b/cura/Arranging/ShapeArray.py
@@ -78,7 +78,7 @@ class ShapeArray:
                 for child in children:
                     # 'Inefficient' combination of convex hulls through known code rather than mess it up:
                     child_hull = child.callDecoration("getConvexHull")
-                    if not child_hull is None:
+                    if child_hull is not None:
                         hull_verts = hull_verts.unionConvexHulls(child_hull)
                     child_hull_head = child.callDecoration("getConvexHullHead") or child_hull
                     if not child_hull_head is None: