Do not export Answer::value when is None

[imobachgs]

Problem

It is not possible to import the following (valid) configuration:

{
   "questions": {
      "answers": [
         {
            "answer": "yes",
            "class": "storage.activate_multipath"
         }
      ]
   }
}

Agama relies on Axum to parse the request. However, it does an extra validation, exporting the configuration to JSON.
That process produces an invalid configuration.

Solution

Do not export the "value" when it is None.
Short description of the fix.

Testing

• Tested manually