RFR: JDK-8323543: NPE when table items are set to null [v2]

[Carl Döbbelin]

On Wed, 10 Jan 2024 19:09:47 GMT, Carl Döbbelin <duke at openjdk.org> wrote:

>> This PR fixes a nullpointer in TableSkinUtils that occured when the Tables items were null.
>
> Carl Döbbelin has updated the pull request incrementally with one additional commit since the last revision:
> 
>   JDK-8323543: clean up code

Regarding the NPEs: 
- i was able to trigger an exception in TableView:1922
- the code in TableCellBehaviour:70 is only reachable by user interaction with a cell. A cell only exists when a TableView has items. The interaction will never happen while `items` is null, because the code is unreachable in that case

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PR Comment: https://git.openjdk.org/jfx/pull/1329#issuecomment-1887550425