RFR: 8341286: TreeView: visual artifacts when setting new root with null value [v2]

[Andy Goryachev]

On Tue, 29 Jul 2025 11:32:00 GMT, Ziad El Midaoui <zelmidaoui at openjdk.org> wrote:

>> The issue is that when we use null value for root item in a TreeView and then expand the root or change it dynamically there are phantom disclosure nodes that appear incorrectly. 
>> The issue was caused by this line `if (getSkinnable().isEmpty()) return;` in `TreeCellSkin#updateDisclosureNode()` as it prevents the method from running unless the cell's value is not empty and it caused the creation of disclosure nodes visually without any logic behind.
>
> Ziad El Midaoui has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Update TreeCellSkin.java

verified the fix on macOS 15.5 M1.

you may want to remove unnecessary newline in L362.

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Marked as reviewed by angorya (Reviewer).

PR Review: https://git.openjdk.org/jfx/pull/1838#pullrequestreview-3067883646