That is logged inside a try catch like this:
settingLabel = GetGlobalResourceObject(resourceFile, s.SettingName).ToString();
catch (NullReferenceException ex)
log.Error("ModuleSettings.aspx.cs error getting resource for s.SettingName " + s.SettingName, ex);
so you may see it in your log but it should not appear in the page and it should not be causing edit problems. I would look for a different cause or a different error if you are not able to edit.
If you are not using resources, you might try putting "Resource" as the resourceFile in your settings anyway and see if it helps.
Hope it helps,