#7176 add testing for null host DV on DS Create

[sekmiller]

What this PR does / why we need it:
For recent button updates we moved some of the render logic to the DatasetPage bean. This logic assumes that the dataset has an owner (host dataverse). if on create the user decides to null out the host dataverse this logic breaks and the page fails to render. This PR updates the render logic to guard against a null host dataverse.

Which issue(s) this PR closes:

Closes #7176 Create Dataset Validation fails etc.

Special notes for your reviewer:

Suggestions on how to test this:

Does this PR introduce a user interface change? If mockups are available, please link/include them here:
No
Is there a release notes update needed for this change?:
No

Additional documentation:
None

[coveralls]

Coverage decreased (-0.002%) to 19.559% when pulling f1a4a42 on 7176-create-ds-validation into 90c675d on develop.

[scolapasta]

I get the goal of this PR. I just don't love null checks for things that should never be null (it can hide real issues). I wonder if a better solution would be to disconnect the ui field from the dataset directly, and to set the owner from the field on save (additionally there can be validation to make sure a host dataverse is selected). @sekmiller what do you think? (one concern is that we'll never clean this up later)

[sekmiller]

OK. I'll try to handle it that way.

[sekmiller]

Abandoning in favor of another approach