Crash when executing a trade

```

Noble Fates Critical Error:

NullReferenceException: Object reference not set to an instance of an object

UITradeScreenWindowContents.ExecuteTrade () (at <955b772a38784a09a701fe2c1b71b2af>:0)

UIElementBehavior.LeftClick () (at <955b772a38784a09a701fe2c1b71b2af>:0)

UIButtonBehavior.LeftClick () (at <955b772a38784a09a701fe2c1b71b2af>:0)

UIElementBehavior.OnPointerUp (UnityEngine.EventSystems.PointerEventData eventData) (at <955b772a38784a09a701fe2c1b71b2af>:0)

UnityEngine.EventSystems.ExecuteEvents.Execute (UnityEngine.EventSystems.IPointerUpHandler handler, UnityEngine.EventSystems.BaseEventData eventData) (at <9e70ad52c23e43edb28b88f7fbf10373>:0)

UnityEngine.EventSystems.ExecuteEvents.Execute[T] (UnityEngine.GameObject target, UnityEngine.EventSystems.BaseEventData eventData, UnityEngine.EventSystems.ExecuteEvents+EventFunction`1[T1] functor) (at <9e70ad52c23e43edb28b88f7fbf10373>:0)

UnityEngine.EventSystems.EventSystem:Update()

```