Description

using System.Text.Json;
using System.Text.Json.Serialization;

ClassB b = new ClassB();
var test = JsonSerializer.Serialize(b);
Console.ReadLine();

public class ClassA
{
    [JsonIgnore]
    public string test { get; set; }
}

public class ClassB : ClassA
{
    [JsonIgnore]
    public new string test { get; set; }
}

The above code will throw an exception: System.ArgumentException:“An item with the same key has already been added. Key: test”

When both base class and derived class has a property with the same name (derived class using new to override property in base class), and both of this two properties marked as [JsonIgnore], Serialize function throw this exception.