I can’t seem to get Plotly.js’ contour plot to look correct with a null area.

I was able to get my first contour map to display the way I wanted for a unit square. Top left quadrant is white (null), bottom left quadrant is horizontal levels decreasing in value until 0 at y = 0.5, top left quadrant is vertical levels increasing in value from 0 at x = 0.5, and finally bottom right quadrant is diagonal lines increase from 0 at x = 0.5:

https://lbmaps.web.app/

I accomplished this with the following data:

```
{ x: [0, 0.5, 0.5, 1]
, y: [0, 0.5, 0.5, 1]
, z:
[ [0.5, 0.5, 0.5, 1]
, [0, 0, 0, 0.5]
, [null, null, 0, 0.5]
, [null, null, 0, 0.5]
]
}
```

I had to duplicate parts to get the contour plot to display the null area properly. Otherwise the top of the lower left quadrant bleeds into the null area. Unfortunately, I have not been able to successfully do the same for a simpler contour plot where the diagonal levels increase from 0 at y = x towards the bottom right corner. You can see this by clicking the “Observational probabilities?” checkbox. The blue bleeds into the null area.

Any way to fix this?