Adds new JsonConverter for special ints which can have "none" as value, too.

src/Api/Set.cs

@@ -22,6 +22,8 @@ public class Set : EndpointObject
 
     public string? Language { get; set; }
 
+    [JsonNumberHandling(JsonNumberHandling.AllowReadingFromString)]
+    [JsonConverter(typeof(NoneIntJsonConverter))] // set hashes in card objects sometimes have "none" as year.
     public int Year { get; set; }
 
     // TODO: According to documentation the property currently is not supported.

src/Utils/JsonConverter/NoneIntJsonConverter.cs

@@ -0,0 +1,36 @@
+using System;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace JpnCardsPokemonSdk.Utils.JsonConverter;
+
+internal class NoneIntJsonConverter : JsonConverter<int>
+{
+    public override int Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+    {
+        if (reader.TokenType == JsonTokenType.String)
+        {
+            var valueStr = reader.GetString();
+
+            if (valueStr?.Equals("none", StringComparison.InvariantCultureIgnoreCase) ?? true)
+                return -1;
+
+            if (int.TryParse(valueStr, out var number))
+                return number;
+        }
+        else if (reader.TokenType == JsonTokenType.Number)
+        {
+            return reader.GetInt32();
+        }
+
+        return -1;
+    }
+
+    public override void Write(Utf8JsonWriter writer, int value, JsonSerializerOptions options)
+    {
+        if (value >= 0)
+            writer.WriteNumberValue(value);
+        else
+            writer.WriteStringValue("non");
+    }
+}