diff --git a/logic/Gaming/AttackManager.cs b/logic/Gaming/AttackManager.cs
index 0db4748..9b9fc1e 100644
--- a/logic/Gaming/AttackManager.cs
+++ b/logic/Gaming/AttackManager.cs
@@ -48,7 +48,7 @@ namespace Gaming
                 {
                     case GameObjType.Character:
 
-                        if ((!(((Character)objBeingShot).IsGhost())) && bullet.Parent.IsGhost())
+                        if ((!(((Character)objBeingShot).IsGhost())) && bullet.Parent!.IsGhost())
                         {
                             characterManager.BeAttacked((Student)objBeingShot, bullet);
                         }
@@ -57,7 +57,7 @@ namespace Gaming
                         break;
                     case GameObjType.Generator:
                         if (bullet.CanBeBombed(GameObjType.Generator))
-                            ((Generator)objBeingShot).Repair(-bullet.AP * GameData.factorDamageGenerator, (Character)bullet.Parent);
+                            ((Generator)objBeingShot).Repair(-bullet.AP * GameData.factorDamageGenerator, (Character)bullet.Parent!);
                         break;
                     default:
                         break;
@@ -101,12 +101,12 @@ namespace Gaming
                 {
                     if (objBeingShot == null)
                     {
-                        characterManager.BackSwing((Character)bullet.Parent, bullet.Backswing);
+                        characterManager.BackSwing((Character)bullet.Parent!, bullet.Backswing);
                         return;
                     }
 
                     BombObj(bullet, objBeingShot);
-                    characterManager.BackSwing((Character)bullet.Parent, bullet.RecoveryFromHit);
+                    characterManager.BackSwing((Character)bullet.Parent!, bullet.RecoveryFromHit);
                     return;
                 }
 
@@ -122,7 +122,7 @@ namespace Gaming
 
                 if (bullet.TypeOfBullet == BulletType.BombBomb && objBeingShot != null)
                 {
-                    bullet.Parent.BulletOfPlayer = BulletType.JumpyDumpty;
+                    bullet.Parent!.BulletOfPlayer = BulletType.JumpyDumpty;
                     Debugger.Output(bullet.Parent, bullet.Parent.CharacterType.ToString() + " " + bullet.Parent.BulletNum.ToString());
                     Attack((Character)bullet.Parent, bullet.FacingDirection.Angle() + Math.PI / 2.0);
                     Attack((Character)bullet.Parent, bullet.FacingDirection.Angle() + Math.PI * 3.0 / 2.0);
@@ -159,10 +159,10 @@ namespace Gaming
 
                 if (objBeingShot == null)
                 {
-                    characterManager.BackSwing((Character)bullet.Parent, bullet.Backswing);
+                    characterManager.BackSwing((Character)bullet.Parent!, bullet.Backswing);
                 }
                 else
-                    characterManager.BackSwing((Character)bullet.Parent, bullet.RecoveryFromHit);
+                    characterManager.BackSwing((Character)bullet.Parent!, bullet.RecoveryFromHit);
             }
 
             public bool Attack(Character player, double angle)
diff --git a/logic/Gaming/CharacterManager .cs b/logic/Gaming/CharacterManager .cs
index c7aefaf..2a12664 100644
--- a/logic/Gaming/CharacterManager .cs	
+++ b/logic/Gaming/CharacterManager .cs	
@@ -25,11 +25,11 @@ namespace Gaming
                     switch (player.PlayerState)
                     {
                         case PlayerStateType.OpeningTheChest:
-                            ((Chest)player.WhatInteractingWith).StopOpen();
+                            ((Chest)player.WhatInteractingWith!).StopOpen();
                             player.ChangePlayerState(value, gameObj);
                             break;
                         case PlayerStateType.OpeningTheDoorway:
-                            Doorway doorway = (Doorway)player.WhatInteractingWith;
+                            Doorway doorway = (Doorway)player.WhatInteractingWith!;
                             doorway.OpenDegree += gameMap.Timer.nowTime() - doorway.OpenStartTime;
                             doorway.OpenStartTime = 0;
                             player.ChangePlayerState(value, gameObj);
@@ -302,7 +302,7 @@ namespace Gaming
                 if (character.CanBeAwed())
                 {
                     if (BeStunned(character, GameData.basicStunnedTimeOfStudent))
-                        bullet.Parent.AddScore(GameData.TrickerScoreStudentBeStunned(GameData.basicStunnedTimeOfStudent));
+                        bullet.Parent!.AddScore(GameData.TrickerScoreStudentBeStunned(GameData.basicStunnedTimeOfStudent));
                     return true;
                 }
                 return false;
@@ -321,7 +321,7 @@ namespace Gaming
                 Debugger.Output(student, "is being shot!");
 #endif
                 if (student.NoHp()) return;  // 原来已经死了
-                if (!bullet.Parent.IsGhost()) return;
+                if (!bullet.Parent!.IsGhost()) return;
 
                 if (student.CharacterType == CharacterType.StraightAStudent)
                 {
@@ -413,9 +413,10 @@ namespace Gaming
                 }
                 if (player.CharacterType == CharacterType.Robot)
                 {
-                    if (((Golem)player).Parent != null && ((Golem)player).Parent.CharacterType == CharacterType.TechOtaku)
+                    var parent = ((Golem)player).Parent;
+                    if (parent != null && parent.CharacterType == CharacterType.TechOtaku)
                     {
-                        ((SummonGolem)(((Golem)player).Parent.FindIActiveSkill(ActiveSkillType.SummonGolem))).GolemSummoned = null;
+                        ((SummonGolem)(parent.FindIActiveSkill(ActiveSkillType.SummonGolem))).GolemSummoned = null;
                         player.FindIActiveSkill(ActiveSkillType.UseRobot).IsBeingUsed = false;
                     }
                     return;