NullableConverter.cs

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namespace System.Text.Json.Serialization.Converters;
 
internal sealed class NullableConverter<T> : JsonConverter<T?> where T : struct
{
    private readonly JsonConverter<T> _converter;
 
    public NullableConverter(JsonConverter<T> converter)
    {
        _converter = converter;
        IsInternalConverterForNumberType = converter.IsInternalConverterForNumberType;
    }
 
    public override T? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        if (reader.TokenType == JsonTokenType.Null)
        {
            return null;
        }
        return _converter.Read(ref reader, typeof(T), options);
    }
 
    public override void Write(Utf8JsonWriter writer, T? value, JsonSerializerOptions options)
    {
        if (!value.HasValue)
        {
            writer.WriteNullValue();
        }
        else
        {
            _converter.Write(writer, value.Value, options);
        }
    }
 
    internal override T? ReadNumberWithCustomHandling(ref Utf8JsonReader reader, JsonNumberHandling numberHandling, JsonSerializerOptions options)
    {
        if (reader.TokenType == JsonTokenType.Null)
        {
            return null;
        }
        return _converter.ReadNumberWithCustomHandling(ref reader, numberHandling, options);
    }
 
    internal override void WriteNumberWithCustomHandling(Utf8JsonWriter writer, T? value, JsonNumberHandling handling)
    {
        if (!value.HasValue)
        {
            writer.WriteNullValue();
        }
        else
        {
            _converter.WriteNumberWithCustomHandling(writer, value.Value, handling);
        }
    }
}