Create/Update doesn't work propertly

[5ORBEX]

Hi guys.
I work on the C# transfer app that should export some data from one database and import it to Odoo. And I use this library. It helps me very lot. But I encountered some strange behavior.

I have a ResPartnerOdooModel:

[OdooTableName("res.partner")]
[JsonConverter(typeof(OdooModelConverter))]
public class ResPartnerOdooModel : IOdooModel
{
    [JsonProperty("id")]
    public long Id { get; set; }

    [JsonProperty("name")]
    public string Name { get; set; }

    [JsonProperty("country_id")]
    public long? CountryId { get; set; }
}

In my code, I have some method that returns the ID of the record from the Odoo database for the specific country by country name:

So what happened?
In my data from the source database, there are 2 records with the same name but in the first record Country = "NULL", and in the second record Country = "United States". The code for the "United States" in the Odoo database is 233.
So, I import the first record:

var model = OdooDictionaryModel.Create(() => new ResPartnerOdooModel()
{
    Name = name,
    CountryId = null,
});

var createResult = await repository.CreateAsync(model);
if (createResult.Succeed)
{
    // ID of the created record
    long createdRecordId = createResult.Value;
}

All good. I see the correct record in the Odoo database.
After this I check by Name if I already have the imported record:

var filter = OdooFilter<ResPartnerOdooModel>.Create().EqualTo(r => r.Name, name);
var partnerResult = await repository.Query().Where(filter).FirstOrDefaultAsync();
var partnerId = partnerResult.Value.Id;

It returns the correct ID of the first created record in the Odoo database.
After this, I try to update this record with new data, where CountryId = 233:

var model = OdooDictionaryModel.Create(() => new ResPartnerOdooModel()
{
    Name = name,
    CountryId = 233,
});

var createResult = await repository.UpdateAsync(model, partnerId);

But after calling the Update method I still see the record in the database where the cell in the "country_id" = "NULL".
I also tried to replace the Update method by calling:

var deleteResult = await repository.DeleteAsync(partnerId);
if (deleteResult.Succeed && deleteResult.Value)
{
    var createResult = await repository.CreateAsync(model);
}

It removes the old record and should create a new record with CountryId = 233. And I see that record was created, it has a new "id" and new "create_date" values, but still "country_id" = "NULL".

Why it doesn't want to update the "country_id"?