Memory leak due to GridPartsResizeBehavior never disposes

[izaksuilov]

If i set GridPartsResizeBehavior.SetTarget(_grid, this); and I want to delete this behavior I should write smt like this GridPartsResizeBehavior.SetTarget(_grid, null!);

Even though I'm trying to set Target to null in this case, the previous behavior should still be disposed due to the code:
https://github.com/npolyak/NP.Ava.Visuals/blob/main/src/Behaviors/GridPartsResizeBehavior.cs#L147-L151

//...
behavior?.Dispose();
if (targetControl != null)
{
    behavior = grid.Children.AddBehavior(OnChildAdded, OnChildRemoved);
}
//...

BUT! If you decompile you can see that behavior isn't saved and it is always null so nothing is disposed (((IDisposable)null)?.Dispose();)

private static void OnTargetChanged(AvaloniaPropertyChangedEventArgs<Control> changedArgs)
{
	Grid grid = (Grid)changedArgs.Sender;
	Func<Point, double> shiftConverter = null;
	double initialSplitterPosition = 0.0;
	double initialShift = 0.0;
	double minChange = 0.0;
	double maxChange = 0.0;
	GridSplitter gridSplitter = null;
	Control targetControl = changedArgs.NewValue.Value;
	((IDisposable)null)?.Dispose();
	if (targetControl != null)
	{
		grid.Children.AddBehavior(OnChildAdded, OnChildRemoved);
	}
       //...

Please fix this cause it leads to memory leaks