#8667 fix null pointer exception

[pkiraly]

What this PR does / why we need it:

To prevent a NullPointerException.

Which issue(s) this PR closes:

Closes #8667

Special notes for your reviewer:
In the method I did some code format change, because it was not clear at some points where the opening brackets end.

Suggestions on how to test this:
Do

wget https://gdcc.github.io/dataverse-external-vocab-support/examples/config/cvoc-conf.json
curl -X PUT --upload-file cvoc-conf.json http://localhost:8080/api/admin/settings/:CVocConf

and compare before/after PR w.r.t. the log and site functionality (see issue).

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:
No

[qqmyers]

Makes sense - a straight-forward improvement in handling bad CVOC input.

It would be good to add specific instructions for how to cause/test this issue - in the latest release with standard metadata blocks - presumably you need a CVOC config file that has an entry for a non-existent field so dft is null - can you provide a file for this?

[pkiraly]

@qqmyers What I did is simply these two commands:

wget https://gdcc.github.io/dataverse-external-vocab-support/examples/config/cvoc-conf.json
curl -X PUT --upload-file cvoc-conf.json http://localhost:8080/api/admin/settings/:CVocConf

Sorry, I do not get what file do you suggest exactly. Could you give a brief explanation? I can put these commands to a file, but what should be its name, and where to put it?

[qqmyers]

Those two commands are enough - I wanted to make sure that the cvoc-conf.json you used is accessible (and it is at https://gdcc.github.io/dataverse-external-vocab-support/examples/config/cvoc-conf.json) and that that would demonstrate the issue with the develop branch (it should because "field-name": "compoundDemo" doesn't exist in any of the standard metadata blocks.)