public override int GetHashCode()
 {
     unchecked
     {
         return(((_oldNode != null ? _oldNode.GetHashCode() : 0) * 397) ^ (_newNode != null ? _newNode.GetHashCode() : 0));
     }
 }
 public override int GetHashCode()
 {
     return(_node != null ? _node.GetHashCode() : 0);
 }