[DataGrid] Removes <GridCell /> fallback to valueToRender on null children

[MBilalShafi]

Closes #5612

• Fix the issue
• Test the fix
• Fix other impacting tests

Changelog

Breaking changes

• Passing children as null to <GridCell /> will not render valueToRender anymore

[mui-bot]

	Messages
📖	Netlify deploy preview: https://deploy-preview-7023--material-ui-x.netlify.app/

These are the results for the performance tests:

Test case	Unit	Min	Max	Median	Mean	σ
Filter 100k rows	ms	691.1	1,227.9	691.1	937.58	193.502
Sort 100k rows	ms	660.3	1,253.1	1,253.1	959.08	213.493
Select 100k rows	ms	215.5	326.2	276.8	282.6	39.25
Deselect 100k rows	ms	199.5	278.3	219.7	225.78	27.463

Generated by 🚫 dangerJS against 3d15535

[MBilalShafi]

@mui/x Team, I am not sure if this should be added to the migration guide, I mean could there be any possibility someone is returning null to have valueToRender shown?

[cherniavskii]

could there be any possibility someone is returning null to have valueToRender shown?

I can think of only one use case - returning the custom component conditionally and falling back to the default one:

const renderCell = () => {
  if (condition) {
    return <CustomComponent />;
  }
  return null;
}

I think it's worth mentioning in the migration guide with a suggestion to return undefined instead to keep the same behavior.