diff --git a/cura/Machines/ContainerTree.py b/cura/Machines/ContainerTree.py
index bfede3d977..699c621fbe 100644
--- a/cura/Machines/ContainerTree.py
+++ b/cura/Machines/ContainerTree.py
@@ -83,7 +83,7 @@ class ContainerTree:
     #
     #   This handles the lazy loading of MachineNodes.
     class MachineNodeMap:
-        def __init__(self):
+        def __init__(self) -> None:
             self._machines = {}
 
         ##  Returns whether a printer with a certain definition ID exists. This
@@ -152,4 +152,4 @@ class ContainerTree:
                     continue
                 definition_id = stack.definition.getId()
                 if not self.tree_root.machines.is_loaded(definition_id):
-                    _ = self.tree_root.machines[definition_id]
\ No newline at end of file
+                    _ = self.tree_root.machines[definition_id]