diff --git a/plugins/UM3NetworkPrinting/src/ClusterUM3OutputDevice.py b/plugins/UM3NetworkPrinting/src/ClusterUM3OutputDevice.py
index 08592df603..60474156a8 100644
--- a/plugins/UM3NetworkPrinting/src/ClusterUM3OutputDevice.py
+++ b/plugins/UM3NetworkPrinting/src/ClusterUM3OutputDevice.py
@@ -609,6 +609,17 @@ class ClusterUM3OutputDevice(NetworkedPrinterOutputDevice):
         material_manager = CuraApplication.getInstance().getMaterialManager()
         material_group_list = material_manager.getMaterialGroupListByGUID(material_data["guid"])
 
+        # This can happen if the connected machine has no material in one or more extruders (if GUID is empty), or the		
+        # material is unknown to Cura, so we should return an "empty" or "unknown" material model.		
+        if material_group_list is None:
+            material_name = "Empty" if len(material_data["guid"]) == 0 else "Unknown"
+            return MaterialOutputModel(guid = material_data["guid"],
+                                        type = material_data.get("type", ""),
+                                        color = material_data.get("color", ""),
+                                        brand = material_data.get("brand", ""),
+                                        name = material_data.get("name", material_name)
+                                        )
+
         # Sort the material groups by "is_read_only = True" first, and then the name alphabetically.
         read_only_material_group_list = list(filter(lambda x: x.is_read_only, material_group_list))
         non_read_only_material_group_list = list(filter(lambda x: not x.is_read_only, material_group_list))