AutoUpdate of DateTimePoint Series through 'null' causes full series re-draw (Avalonia)

[houstonhaynes]

Describe the bug
When the line series ObservableCollection<DateTimePoint> updates with a 'null' value at the first position RemoveAt(0) the chart performs a full redraw of the series.

To Reproduce
Steps to reproduce the behavior:

1. Build/run my AvaloniaExample app https://github.com/houstonhaynes/Elmish.Avalonia/tree/main/src/Samples/AvaloniaExample
2. Click on AutoUpdate (null values are inserted 5% of the time)
3. Observe the "gap" reaching the left edge of the display area of the chart
4. Note that when the last value before the gap is removed that the full series re-draws in the chart

Expected behavior
The chart should continue to "slide left" smoothly without a full redraw of the series.
Along those lines, the series should visually "hold" the position for the null value so that "slide" increment remains a consistent cadence.

Screenshots
See attached video

Screen.Recording.2023-06-27.at.11.23.15.AM.mov

Desktop (please complete the following information):

• OS: MacOS M1
• Browser: N/A
• Version 2.0.0-beta.801

Additional context
LiveCharts is AMAZING! 😺 👍

[beto-rodriguez]

Th referenced commit fixes this issue, but the algorithm needs a review, this issue is still present when we insert a null instance. As a temporal solution this seems ok, but we can improve this.

[beto-rodriguez]

[houstonhaynes]

This is so great - everythig at this level feels like an interim step. 👍