Fix: Domain update issue when null properties are saved

[ezilber-akamai-zz]

📝 Description

Fixed issue when attempting to update Domain with some null values.

✔️ How to Test

Run tox.

Ticket: TPT-1871
Resolves #208

[lgarber-akamai]

@ezilber-akamai Maybe we could add a nullable field attribute corresponding to the nullable attributes in our API spec/docs, where these fields would always be included in .save() PUT requests. This would allow PUT endpoints that accept null as a valid value (e.g. IP update) to function as expected.

For example, the IP RDNS field here could look like this:

"rdns": Property(mutable=True, nullable=True),

and could then be included in PUT request bodies regardless of whether it's null or defined

{
    "rdns": null
}

[ezilber-akamai-zz]

@lgarber-akamai Great idea! Is this something we would want to implement across the repo? If so, should we consider creating a separate ticket for this?