Suggested changes

CURA-9412

plugins/3MFWriter/ThreeMFWriter.py

@@ -12,6 +12,7 @@ from UM.Application import Application
 from UM.Message import Message
 from UM.Resources import Resources
 from UM.Scene.SceneNode import SceneNode
+from UM.Settings.ContainerRegistry import ContainerRegistry
 from UM.Settings.EmptyInstanceContainer import EmptyInstanceContainer
 
 from cura.CuraApplication import CuraApplication
@@ -269,7 +270,7 @@ class ThreeMFWriter(MeshWriter):
                 # Don't export materials not in use
                 continue
 
-            if type(extruder.material) is EmptyInstanceContainer:
+            if isinstance(extruder.material, type(ContainerRegistry.getInstance().getEmptyInstanceContainer())):
                 # This is an empty material container, no material to export
                 continue