Fix some typing issues

cura/CuraApplication.py

@@ -1368,16 +1368,19 @@ class CuraApplication(QtApplication):
 
         for node in nodes:
             mesh_data = node.getMeshData()
-            if mesh_data and mesh_data.getFileName():
-                job = ReadMeshJob(mesh_data.getFileName())
-                job._node = node  # type: ignore
-                job.finished.connect(self._reloadMeshFinished)
-                if has_merged_nodes:
-                    job.finished.connect(self.updateOriginOfMergedMeshes)
-
-                job.start()
-            else:
-                Logger.log("w", "Unable to reload data because we don't have a filename.")
+
+            if mesh_data:
+                file_name = mesh_data.getFileName()
+                if file_name:
+                    job = ReadMeshJob(file_name)
+                    job._node = node  # type: ignore
+                    job.finished.connect(self._reloadMeshFinished)
+                    if has_merged_nodes:
+                        job.finished.connect(self.updateOriginOfMergedMeshes)
+
+                    job.start()
+                else:
+                    Logger.log("w", "Unable to reload data because we don't have a filename.")
 
     @pyqtSlot("QStringList")
     def setExpandedCategories(self, categories: List[str]) -> None:

cura/Scene/ConvexHullNode.py

@@ -1,6 +1,6 @@
 # Copyright (c) 2015 Ultimaker B.V.
 # Cura is released under the terms of the LGPLv3 or higher.
-from typing import Optional
+from typing import Optional, TYPE_CHECKING
 
 from UM.Application import Application
 from UM.Math.Polygon import Polygon
@@ -11,6 +11,9 @@ from UM.Math.Color import Color
 from UM.Mesh.MeshBuilder import MeshBuilder  # To create a mesh to display the convex hull with.
 from UM.View.GL.OpenGL import OpenGL
 
+if TYPE_CHECKING:
+    from UM.Mesh.MeshData import MeshData
+
 
 class ConvexHullNode(SceneNode):
     shader = None  # To prevent the shader from being re-built over and over again, only load it once.
@@ -43,7 +46,7 @@ class ConvexHullNode(SceneNode):
 
         # The node this mesh is "watching"
         self._node = node
-        self._convex_hull_head_mesh = None
+        self._convex_hull_head_mesh = None  # type: Optional[MeshData]
 
         self._node.decoratorsChanged.connect(self._onNodeDecoratorsChanged)
         self._onNodeDecoratorsChanged(self._node)