Null points render & cause cursor change on mouseover

[Fedjmike]

Putting the following code into https://c3js.org/samples/chart_scatter.html:

var chart = c3.generate({
    data: {
        columns: [
            ['data1', 30, 200, 100, 400, 150, 250],
            ['data2', 50, null, 10, 40, 15, 25]
        ],
        type: 'scatter'
    }
});

At y=0 and x=1, there is a ghost point corresponding to the null, which is rendered with opacity: 0, but nevertheless causes a cursor change on mouseover.

I'm currently working around this by setting display: none. Using d3 remove() instead causes some flickering re-rendering issues.

• C3 version: 0.7.15
• D3 version: 5.8.2
• Browser: Chrome 80.0.3987.116
• OS: OS X 10.15.2