private void Awake()
        {
            collider = GetComponent <Collider2D>();

            if (onTriggerEnter == null)
            {
                onTriggerEnter = new Trigger2DEvent();
            }

            if (onTriggerExit == null)
            {
                onTriggerExit = new Trigger2DEvent();
            }

            if (onTriggerStay == null)
            {
                onTriggerStay = new Trigger2DEvent();
            }

            if (onCollisionEnter == null)
            {
                onCollisionEnter = new Collision2DEvent();
            }

            if (onCollisionExit == null)
            {
                onCollisionExit = new Collision2DEvent();
            }

            if (onCollisionStay == null)
            {
                onCollisionStay = new Collision2DEvent();
            }
        }