System.NullReferenceException: Object reference not set to an instance of an object
at PoliciesPanel.SetParentButton (ColossalFramework.UI.UIButton button) [0x00000] in <filename unknown>:0
at GameMainToolbar.RefreshPanel () [0x00000] in <filename unknown>:0
at (wrapper delegate-invoke) System.Action:invoke_void__this__ ()
at (wrapper delegate-invoke) System.Action:invoke_void__this__ ()
at (wrapper delegate-invoke) System.Action:invoke_void__this__ ()
at (wrapper delegate-invoke) System.Action:invoke_void__this__ ()
at UnlockManager.MilestonesUpdated () [0x00000] in <filename unknown>:0
at UnlockManager.<CheckMilestone>m__167 () [0x00000] in <filename unknown>:0
at ColossalFramework.Threading.Dispatcher+<>c__DisplayClass4.<CreateSafeAction>b__3 () [0x00000] in <filename unknown>:0