Issue #4036: Allow for an empty option in select fields via schema pr…

[stefan-korn]

fixes #4036

• Test coverage exists
• Documentation exists

QA Steps

• create or edit a dataset with an optional list (enum) field (like accrualPeriodicity) and note that there will be an empty option beside the real values in the select dialog
• if you save with the empty option the value should not exist in the json stored

[dafeder]

See my comment on the issue @stefan-korn, I think the proper behavior here is just to add an empty option in the select for any enum that is not required, and make sure the JSON that is produced does not contain the property.

[dafeder]

Looks like we're going a different direction anyway, but not sure where $property->empty_value is supposed to be getting set?

[stefan-korn]

I supposed it to be set in the schema .json file, just like "type", "format", etc. But yes now we are going a different and better way.

[dafeder]

@stefan-korn do you feel up to updating the tests? I think you should be able to see the circleCI results and that the tests are all broken now... fairly trivial to update them to expect this and possibly to confirm the right result for both required and non-required fields, but if you're not familiar with PHPUnit let me know and we can help with that part.

[stefan-korn]

I fixed the tests. The html output itself is not checked I suppose?