diff --git a/cura/Scene/ConvexHullDecorator.py b/cura/Scene/ConvexHullDecorator.py
index 85d1e8e309..a78f559aa1 100644
--- a/cura/Scene/ConvexHullDecorator.py
+++ b/cura/Scene/ConvexHullDecorator.py
@@ -15,8 +15,6 @@ import numpy
 
 from typing import TYPE_CHECKING, Any, Optional
 
-
-
 if TYPE_CHECKING:
     from UM.Scene.SceneNode import SceneNode
     from cura.Settings.GlobalStack import GlobalStack
@@ -35,10 +33,11 @@ class ConvexHullDecorator(SceneNodeDecorator):
 
         # Make sure the timer is created on the main thread
         self._recompute_convex_hull_timer = None  # type: Optional[QTimer]
-        Application.getInstance().callLater(self.createRecomputeConvexHullTimer)
+
+        if Application.getInstance() is not None:
+            Application.getInstance().callLater(self.createRecomputeConvexHullTimer)
 
         self._raft_thickness = 0.0
-        # For raft thickness, DRY
         self._build_volume = Application.getInstance().getBuildVolume()
         self._build_volume.raftThicknessChanged.connect(self._onChanged)
 
@@ -72,7 +71,7 @@ class ConvexHullDecorator(SceneNodeDecorator):
     def __deepcopy__(self, memo):
         return ConvexHullDecorator()
 
-    ##  Get the unmodified 2D projected convex hull of the node
+    ##  Get the unmodified 2D projected convex hull of the node (if any)
     def getConvexHull(self) -> Optional[Polygon]:
         if self._node is None:
             return None
@@ -120,6 +119,7 @@ class ConvexHullDecorator(SceneNodeDecorator):
                 return self._compute2DConvexHull()
         return None
 
+    ##  The same as recomputeConvexHull, but using a timer if it was set.
     def recomputeConvexHullDelayed(self) -> None:
         if self._recompute_convex_hull_timer is not None:
             self._recompute_convex_hull_timer.start()
@@ -142,13 +142,13 @@ class ConvexHullDecorator(SceneNodeDecorator):
         self._convex_hull_node = hull_node
 
     def _onSettingValueChanged(self, key: str, property_name: str) -> None:
-        if property_name != "value": #Not the value that was changed.
+        if property_name != "value":  # Not the value that was changed.
             return
 
         if key in self._affected_settings:
             self._onChanged()
         if key in self._influencing_settings:
-            self._init2DConvexHullCache() #Invalidate the cache.
+            self._init2DConvexHullCache()  # Invalidate the cache.
             self._onChanged()
 
     def _init2DConvexHullCache(self) -> None:
@@ -161,7 +161,7 @@ class ConvexHullDecorator(SceneNodeDecorator):
         self._2d_convex_hull_mesh_world_transform = None
         self._2d_convex_hull_mesh_result = None
 
-    def _compute2DConvexHull(self) -> Polygon:
+    def _compute2DConvexHull(self) -> Optional[Polygon]:
         if self._node.callDecoration("isGroup"):
             points = numpy.zeros((0, 2), dtype=numpy.int32)
             for child in self._node.getChildren():
@@ -188,8 +188,6 @@ class ConvexHullDecorator(SceneNodeDecorator):
 
         else:
             offset_hull = None
-            mesh = None
-            world_transform = None
             if self._node.getMeshData():
                 mesh = self._node.getMeshData()
                 world_transform = self._node.getWorldTransformation()
@@ -242,10 +240,10 @@ class ConvexHullDecorator(SceneNodeDecorator):
             return Polygon(numpy.array(self._global_stack.getHeadAndFansCoordinates(), numpy.float32))
         return Polygon()
 
-    def _compute2DConvexHeadFull(self):
+    def _compute2DConvexHeadFull(self) -> Polygon:
         return self._compute2DConvexHull().getMinkowskiHull(self._getHeadAndFans())
 
-    def _compute2DConvexHeadMin(self):
+    def _compute2DConvexHeadMin(self) -> Polygon:
         headAndFans = self._getHeadAndFans()
         mirrored = headAndFans.mirror([0, 0], [0, 1]).mirror([0, 0], [1, 0])  # Mirror horizontally & vertically.
         head_and_fans = self._getHeadAndFans().intersectionConvexHulls(mirrored)
@@ -276,7 +274,7 @@ class ConvexHullDecorator(SceneNodeDecorator):
         else:
             raise Exception("Unknown bed adhesion type. Did you forget to update the convex hull calculations for your new bed adhesion type?")
 
-        # adjust head_and_fans with extra margin
+        # Adjust head_and_fans with extra margin
         if extra_margin > 0:
             extra_margin_polygon = Polygon.approximatedCircle(extra_margin)
             poly = poly.getMinkowskiHull(extra_margin_polygon)
@@ -354,7 +352,7 @@ class ConvexHullDecorator(SceneNodeDecorator):
             # Limit_to_extruder is set. The global stack handles this then
             return self._global_stack.getProperty(setting_key, prop)
 
-    ##  Returns true if node is a descendant or the same as the root node.
+    ##  Returns True if node is a descendant or the same as the root node.
     def __isDescendant(self, root: "SceneNode", node: "SceneNode") -> bool:
         if node is None:
             return False