use nullptr

field.h

@@ -522,7 +522,7 @@ public:
 	int32 check_spself_from_hand_trigger(const chain& ch) const;
 	int32 is_able_to_enter_bp();
 
-	void add_process(uint16 type, uint16 step, effect* peffect, group* target, ptr arg1, ptr arg2, ptr arg3 = 0, ptr arg4 = 0, void* ptr1 = NULL, void* ptr2 = NULL);
+	void add_process(uint16 type, uint16 step, effect* peffect, group* target, ptr arg1, ptr arg2, ptr arg3 = 0, ptr arg4 = 0, void* ptr1 = nullptr, void* ptr2 = nullptr);
 	int32 process();
 	int32 execute_cost(uint16 step, effect* peffect, uint8 triggering_player);
 	int32 execute_operation(uint16 step, effect* peffect, uint8 triggering_player);