Fix for errors caused by fixing RNA function register flags. Default UIList class now has a dummy draw_item callback. Panel draw_header is now optional (most panel classes don't define it).

release/scripts/startup/bl_ui/__init__.py

@@ -138,6 +138,7 @@ def unregister():
 
 # Define a default UIList, when a list does not need any custom drawing...
 class UI_UL_list(bpy.types.UIList):
-    pass
+    def draw_item(self, context, layout, data, item, icon, active_data, active_propname, index):
+        pass
 
 bpy.utils.register_class(UI_UL_list)

source/blender/makesrna/intern/rna_ui.c

@@ -791,7 +791,7 @@ static void rna_def_panel(BlenderRNA *brna)
 
 	func = RNA_def_function(srna, "draw_header", NULL);
 	RNA_def_function_ui_description(func, "Draw UI elements into the panel's header UI layout");
-	RNA_def_function_flag(func, FUNC_REGISTER);
+	RNA_def_function_flag(func, FUNC_REGISTER_OPTIONAL);
 	parm = RNA_def_pointer(func, "context", "Context", "", "");
 	RNA_def_property_flag(parm, PROP_REQUIRED | PROP_NEVER_NULL);