Fixes #12692

Root Cause

• This issue is caused by PR Enable nullability in remaining DataGridViewCell members #10406，which removes the check whether the control is null before executing OnMouseUp in file DataGridViewCell.cs
  That fix moved the null check for the parent DataGridView to the top of the method. However, the parent can be set to null when this cell (or a row containing it) is deleted. In the user's case the row is deleted when the DGV cell is clicked.

Proposed changes

• Add a check if DataGridView is not null before executing OnMouseUp in function OnMouseUpInternal, because the Parent DataGridView might have been disconnected in the user event handler that is executed before this call, for example if the user clears the DataGridView row.

Customer Impact

• Application crashes when the customer clicks on a DataGridView cell, where previously the content was selected.

Regression?

• Yes, from NET8, introduced by nullability changes in PR Enable nullability in remaining DataGridViewCell members #10406

Risk

• Minimal, we are restoring the previous code, i.e. re-adding a null-check

Screenshots

Before

Object reference not set to an instance of an object exception pops up after clicked the DataGridViewCell content when the function DataGridView1_CellContentClick contains content
DataGridView1.Rows.Clear();
DataGridView1.Rows.Add(1, 0, "ABCD");

After

DataGridView Rows can be cleaned and re-added normally

Test methodology

• Manually, added a unit test

Test environment(s)

• .net 10.0.0-alpha.1.24631.2

Microsoft Reviewers: Open in CodeFlow