Code from documentation fails due to null values

[vi]

The documentation contains this line in a code snippet:

value: (self, rawValue) => "$" + rawValue.toFixed(2),

But the library calls it with a null rawValue, leading to errors in console.

[leeoniya]

ah, yeah. this changed a couple years ago. when there is cursor "un-hover", these functions get called with null to allow custom-setting the legend. see #644.

all the demos which use the value or values options are updated to handle null, e.g. https://leeoniya.github.io/uPlot/demos/area-fill.html