RFR: 8089398: [ChoiceBox, ComboBox] throws NPE on setting value on null selectionModel [v4]

[Marius Hanl]

On Wed, 7 Jul 2021 19:37:23 GMT, Marius Hanl <mhanl at openjdk.org> wrote:

>> This PR fixes multiple NPEs in Choice-and ComboBox, when the selection model is null.
>> 
>> ChoiceBox: 
>> - Null check in **valueProperty()** listener
>> 
>> ComboBox:
>> - Null check in **editableProperty()* listener*
>> - Null check in **valueProperty()** listener
>> - Null check in **ComboBoxListViewSkin#updateValue()**
>> - Null check in **ComboBoxListViewSkin#layoutChildren()**
>> 
>> ~~The tests checks, that no NPE is printed to the console.~
>> Some checks, that the set value is still displayed (either in the ComboBox button cell or the ChoiceBox display label)~~
>
> Marius Hanl has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Fixed NPE for setEditable() and layoutChildren()
>  - removed unneeded button cell in test

> Not aware of such a rule - if we fix code throwing an exception there is not much to assert, except that it fails before and passes after. And paddling back a bit, I think a separate test for the back switch would be overdoing it :)

There is no rule, but in my opinion it's simply better and more meaningful with an assert (maybe this also come's a bit from Sonar �� ). But you are right, the checks are not really needed and thinking about it they can be confusing as well. So I will update the PR. 
But I'm also interested in other opinions. 
It would be perfect for me if we have a nice way to indicate, that a Unit test expects no exception. (I now wrote a comment on every method which triggers the NPE)

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PR: https://git.openjdk.java.net/jfx/pull/557