GREG-21: Various model updates

The commits in this merge request contain changes done to be able to import the test data. It is basically opening up for more fields to be able to be null.

Maybe @jbr also wants to take a quick look to see if he agrees with the fields that now can be null.

greg/api/serializers/person.py

@@ -42,3 +42,18 @@ class PersonIdentitySerializer(serializers.ModelSerializer):
     class Meta:
         model = PersonIdentity
         fields = "__all__"
+
+    def is_duplicate(self, identity_type: str, value: str) -> bool:
+        # Guests may be verified using another unrecognised identification method,
+        # which the sponsor is required to elaborate in the value column.
+        # In this case we cannot assume the union of the identity type and
+        # the value to be unique across all records.
+        if identity_type == PersonIdentity.IdentityType.OTHER:
+            return False
+
+        # If the type is a specific ID type, then duplicates are not expected
+        return (
+            PersonIdentity.objects.filter(type__like=identity_type)
+            .filter(value__like=value)
+            .exists()
+        )