Fix NPE when using row group edit

[antoinebrault]

row group edit happens in my case when my users edit a row group field, and I apply it to all children.

Copy of this PR #3383

[nasreddineskandrani]

Hello @seanlandsman,
Do you think you can find some time to check this PR. It will be really useful for a couple of companies in our area. it's a null pointer..

Thank you very much

[seanlandsman]

@nasreddineskandrani I'll raise with the team - thanks for the PR

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[nasreddineskandrani]

@seanlandsman followup please

[seanlandsman]

Apologies for the delay with this

I've raised AG-3995 our side for this issue and we'll endeavour to get this in as soon as possible.

You can track this issue in our pipeline (it may take a few hours for it to appear there): https://www.ag-grid.com/ag-grid-pipeline/

I'm closing this PR but rest assured that this does not mean we won't be actioning it