[charts] Fix Barchart with empty dataset throwing an error

[JCQuintas]

We just use optional chain and nullchecks as fallbacks.

@alexfauquette Should we add tests for these functions?

Fixes #12462

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[mui-bot]

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[alexfauquette]

I agree it fixes the issue, but I'm wondering why do we have this issue with bar chart and not with line chart? They are super close, so they should have the same behavior with empty dataset.

For the fallback on [null, null] I'm ok, it's the same behavior, but for the use of optional chain I'm wondering if we are missing something since I don't see them used in the line chart

[JCQuintas]

@alexfauquette In the Line chart it is divided into two functions and we check for

https://github.com/JCQuintas/mui-x/blob/3cee37ded0a82ab1b2854fa6f2a430c29c32f090/packages/x-charts/src/LineChart/extremums.ts#L17-L19

if (stackedData.length === 0) {
    return [null, null];
}

also the first ?. there can be removed, the issue only happens because data doesn't exist

[alexfauquette]

Ok, if you want to add test, their is a similar one in the LineChart folder. The only test existing for now

[JCQuintas]

Added tests, odd behaviour is that vertical layout returns [Infinity, -Infinity] while horizontal is returning [null, null]. Doesn't seem to affect anything though

[alexfauquette]

Not that surprising. It comes from Math.min() returning Infinity.

const getBaseExtremum: ExtremumGetter<'bar'> = (params) => {
  const { axis } = params;

  const minX = Math.min(...(axis.data ?? []));
  const maxX = Math.max(...(axis.data ?? []));
  return [minX, maxX];
};

What is more surprising is that those extremes are computed. For "band" and "point" scales, the notion of extreme values does not make sense because they contain categories. So they do not have an notion of order.

In cartesian context, those scales got an early return before the min/max values are used. So they could return wherever they want.

Maybe the correct behavior would be that in vertical it always returns [null, null] but since this value is never used, I don't have strong opinion about it

[oliviertassinari]

Time will tell if this test isn't too low level. Testing public APIs tends to scale better.