Added missing typing

cura/LayerDataDecorator.py

@@ -1,13 +1,23 @@
+from typing import Optional
+
 from UM.Scene.SceneNodeDecorator import SceneNodeDecorator
 
 ## Simple decorator to indicate a scene node holds layer data.
+from cura.LayerData import LayerData
+
+
 class LayerDataDecorator(SceneNodeDecorator):
     def __init__(self):
         super().__init__()
-        self._layer_data = None
+        self._layer_data = None  # type: Optional[LayerData]
         
-    def getLayerData(self):
+    def getLayerData(self) -> Optional[LayerData]:
         return self._layer_data
     
-    def setLayerData(self, layer_data):
-        self._layer_data = layer_data
+    def setLayerData(self, layer_data: LayerData) -> None:
+        self._layer_data = layer_data
+
+    def __deepcopy__(self, memo) -> "LayerDataDecorator":
+        copied_decorator = LayerDataDecorator()
+        copied_decorator.setLayerData(self.getLayerData())
+        return copied_decorator