Fix for issue 8747: date field change causes an uncaught exception

[huangderek02]

Fixes #8747

Short Description

In library mode "biblatex", when user edits the entry's "date" field with an invalid input and clicks somewhere, an uncaught exception of null pointer occurs.

Checklist

• Change in CHANGELOG.md described in a way that is understandable for the average user (if applicable)
• Tests created for changes (if applicable)
• Manually tested changed features in running JabRef (always required)
• Screenshots added in PR description (for UI changes)
• Checked developer's documentation: Is the information available and up to date? If not, I outlined it in this pull request.
• Checked documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request to the documentation repository.

UI changes (takes time to load gif images)

• Before

• Type invalid inputs: nothing happen

• Click somewhere: an exception occured;

• Press Enter: input disappears
  

• After

• Type invalid inputs: show warning icon

• Click somewhere: nothing happens

• Press Enter: input disappears
  

[Siedlerchr]

That is a nice improvement. Regarding invalid inputs, as biblatex supports a couple of more dates, see also #9310 ) can you try to integrate this with JabRef's date time parsing class?

And please take a look at the reviewdog output (Files changed tab)

[xianghao-wang]

That is a nice improvement. Regarding invalid inputs, as biblatex supports a couple of more dates, see also #9310 ) can you try to integrate this with JabRef's date time parsing class?

And please take a look at the reviewdog output (Files changed tab)

Hello, could you help have a look at the new change by adding Date integration to the default string converter? I think the string converter provided by DateEditorViewModel already have worked with Date class code.

[Siedlerchr]

Why did you change this to a generic exception? Exception should be always the most specfic one

[Siedlerchr]

I tested your PR and it looks good so far. Please have a look at the failing checkstyle tests and also the exception handling.
I cannot push to your repo so I can't do this myself