翻牌调用MIAN 的CheckIsGameOver();时候出错了

为什么我翻牌调用：

Camera.main.gameObject.GetComponent<gamemain>().CheckIsGameOver();

就会出现问题说：

NullReferenceException: Object reference not set to an instance of an object
cardfilp+<FlipCardToFront>c__Iterator0.MoveNext () (at Assets/Script/cardfilp.cs:74)
UnityEngine.SetupCoroutine.InvokeMoveNext (IEnumerator enumerator, IntPtr returnValueAddress) (at C:/buildslave/unity/build/Runtime/Export/Coroutines.cs:17)

点一次出现一次这个DUBUG