Update hierarchy pane when renaming a group

addons/material_maker/engine/gen_graph.gd

@@ -42,6 +42,10 @@ func get_type() -> String:
 func get_type_name() -> String:
 	return label
 
+func set_type_name(l) -> void:
+	if l !=label:
+		label = l
+		emit_hierarchy_changed()
 
 func toggle_editable() -> bool:
 	editable = !editable

material_maker/graph_edit.gd

@@ -352,7 +352,7 @@ func on_ButtonUp_pressed() -> void:
 		call_deferred("update_view", generator.get_parent())
 
 func _on_Label_text_changed(new_text) -> void:
-	generator.label = new_text
+	generator.set_type_name(new_text)
 
 # Create subgraph
 

material_maker/preview/preview_3d.gd

@@ -54,7 +54,9 @@ func _on_Rotate_toggled(button_pressed) -> void:
 		$MaterialPreview/Preview3d/ObjectRotate.stop(false)
 
 func get_materials() -> Array:
-	return [ current_object.get_surface_material(0) ]
+	if current_object != null:
+		return [ current_object.get_surface_material(0) ]
+	return []
 
 func on_gui_input(event) -> void:
 	if event is InputEventMouseButton: