Backward incompatibility issue between 13.0.1 and 13.0.2

[Augment1n]

Dear Newtonsoft team,

unfortunately there is a compatibility problem between 13.0.1 and 13.0.2.

• 13.0.1 is serializing 00:00:00 TimeOnly as empty strings. And the deserializing is working from an empty string to 00:00:00.
• But in 13.0.2 an empty string is not deserializable to 00:00:00 TimeOnly.

(meanwhile the serialization result is different too, but I do not care about that one)

I attached a minimal working example.
Just open the TimeOnlySerialization/TimeOnlySerialization.sln and run the 2 separate projects and see the console output!

MinimalWorkingExample.zip

Thank you in advance!

[Augment1n]

A custom TimeOnlyConverter solves the issue for simple TimeOnly fields.
But if the TimeOnly is a dictionary key, then it does not.

[Augment1n]

Our workaround:

public class TimeOnlyKeyedImmutableSortedDictionary<TValue> : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof(IDictionary) &&
               objectType.GenericTypeArguments[0] == typeof(TimeOnly) &&
               objectType.GenericTypeArguments[1] == typeof(TValue);
    }

    public override object? ReadJson(JsonReader reader, Type objectType, object? existingValue,
        JsonSerializer serializer)
    {
        var returnValue = new Dictionary<TimeOnly, TValue>();

        if (reader.TokenType != JsonToken.StartObject)
        {
            return returnValue.ToImmutableSortedDictionary();
        }

        reader.Read();

        while (reader.TokenType != JsonToken.EndObject)
        {
            if (reader.TokenType == JsonToken.PropertyName)
            {
                var key = reader.Value?.ToString() ?? "";

                var timeKey = string.IsNullOrEmpty(key)
                    ? new TimeOnly(0, 0, 0)
                    : TimeOnly.Parse(key, CultureInfo.InvariantCulture);

                // Move to value
                reader.Read();
                var value = serializer.Deserialize<TValue>(reader);

                ArgumentNullException.ThrowIfNull(value, nameof(value));
                returnValue[timeKey] = value;
            }

            reader.Read(); // Move to next property or end object
        }

        return returnValue.ToImmutableSortedDictionary();
    }

    public override void WriteJson(JsonWriter writer, object? value, JsonSerializer serializer)
    {
        if (value is not ImmutableSortedDictionary<TimeOnly, TValue> currentValue)
        {
            return;
        }

        writer.WriteStartObject();

        foreach (var kvp in currentValue)
        {
            writer.WritePropertyName(kvp.Key.ToString("HH:mm:ss"));
            serializer.Serialize(writer, kvp.Value);
        }

        writer.WriteEndObject();
    }
}

Register the converter:

new JsonSerializerSettings
        {
            Converters = new List<JsonConverter>
            {
                new TimeOnlyKeyedImmutableSortedDictionary<KpiRecordInternal.ShiftKpi>()
            }
        };

then you can use it like this:

[JsonConverter(typeof(TimeOnlyKeyedImmutableSortedDictionary<ShiftKpi>))]
public ImmutableSortedDictionary<TimeOnly, ShiftKpi> Shifts { get; init; } =
    ImmutableSortedDictionary<TimeOnly, ShiftKpi>.Empty;