Code cleanup

Core/Data/BotUserValue.cs

@@ -4,6 +4,7 @@ using System.Diagnostics.CodeAnalysis;
 using System.IO;
 using System.Runtime.Serialization.Formatters.Binary;
 using System.Text.Json;
+using System.Text.Json.Serialization;
 using System.Xml.Serialization;
 
 namespace Kruzya.TelegramBot.Core.Data
@@ -35,7 +36,7 @@ namespace Kruzya.TelegramBot.Core.Data
         public void SetValue<T>(T value)
         {
             Value = JsonSerializer.SerializeToUtf8Bytes(value, new JsonSerializerOptions { WriteIndented = false, 
-                IgnoreNullValues = true });
+                DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull });
             ValueType = value.GetType().FullName;
         }
     }