<Class> is not registered in this resolver(EnumUnderlyingValueResolver). An exception occurs while serializing an enum as number

[armanzakinyan]

I have these classes below.

[DataContract]
public class Physics
{
    [DataMember]
    public string Lecturer { get; set; }

    [DataMember]
    public WeekDays WeekDay { get; set; }
}

[DataContract]
public enum WeekDays : byte
{
    [EnumMember]
    Monday = 1,

    [EnumMember]
    Tuesday,

    [EnumMember]
    Wednesday,

    [EnumMember]
    Thursday,

    [EnumMember]
    Friday,

    [EnumMember]
    Saturday,

    [EnumMember]
    Sunday
}


Here is my Main() method.

static void Main(string[] args)
    {
        Physics physics_1 = new Physics { Lecturer = "Andrew", WeekDay = WeekDays.Monday };
        var v1 = JsonSerializer.Serialize(physics_1, EnumResolver.UnderlyingValue);
        Console.WriteLine(Encoding.UTF8.GetString(v1));
    }


I want to serialize a Physics object and also I want an enum member of Physics to be a number. While using EnumResolver.UnderlyingValue I got this `exception.`
Physics is not registered in this resolver. resolver:EnumUnderlyingValueResolver