Fix/contact and person attributes can be null

[Zandv320]

Description

The NDW have performed critical changes in their API. a lot of contact attributes are now nullable, also the prefix attribute of a person can now be null. The same goes for remarks.

The above information has been verified by the NDW

Motivation and context

The package crashes now when trying to import Melvin data, since these fields are in almost every situation, its critical that this is resolved quickly.

If it fixes an open issue, please link to the issue here (if you write fixes #num
or closes #num, the issue will be automatically closed when the pull is accepted.)

How has this been tested?

I have ran a test importing the data. Alot of situations had null values for the above fields
Running the integration tests will show that it now works again

Types of changes

What types of changes does your code introduce? Put an x in all the boxes that apply:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

Please, please, please, don't send your pull request until all of the boxes are ticked. Once your pull request is created, it will trigger a build on our continuous integration server to make sure your tests and code style pass.

• I have read the CONTRIBUTING document.
• My pull request addresses exactly one patch/feature.
• I have created a branch for this patch/feature.
• Each individual commit in the pull request is meaningful.
• I have added tests to cover my changes.
• If my change requires a change to the schema, I have updated it accordingly.
• If my change requires a change to the documentation, I have updated it accordingly.

If you're unsure about any of these, don't hesitate to ask. We're here to help!

[JaZo]

This property is an array, so a fallback to an empty string is a little odd here.