AutoMapper Map() returns wrong values

Question

I have a mapping of a class MyClass to the same class MyClass .

The class has a List<T> property in it. The List<T> is NULL before the map.

After the mapped with AutoMapper , the List<T> is not NULL anymore. ( AllowNullDestinationValues does nothing here ...)

Is this intentional or a bug ? Am I missing some configuration step ?

using System.Collections.Generic;
using System.Diagnostics;
using AutoMapper;

namespace ConsoleApplication1
{
    public class MyClass
    {
        public string Label { get; set; }

        public List<int> Numbers { get; set; }
    }

    class Program
    {
        static void Main(string[] args)
        {
            Mapper.CreateMap<MyClass, MyClass>();
            MyClass obj1 = new MyClass { Label = "AutoMapper Test" };
            MyClass obj2 = new MyClass();
            Mapper.Map(obj1, obj2);

            Debug.Assert(obj2 != null && obj2.Numbers == null, "FAILED");
        }
    }
}

I use the AutoMapper v4.1.1 from NuGet.

Answer 1

By default, AutoMapper will map a null collection to an empty collection instead. You can modify this by creating your own AutoMapper profile for configuration.

Take a look at the code below.

public class MyClass
{
    public string Label { get; set; }

    public List<int> Numbers { get; set; }
}
class Program
{
    static void Main(string[] args)
    {
        Mapper.AddProfile<MyProfile>(); // add the profile
        MyClass obj1 = new MyClass { Label = "AutoMapper Test" };
        MyClass obj2 = new MyClass();
        Mapper.Map(obj1, obj2);

        Debug.Assert(obj2 != null && obj2.Numbers == null, "FAILED");
    }
}

public class MyProfile : Profile
{
    protected override void Configure()
    {
        AllowNullCollections = true;
        CreateMap<MyClass, MyClass>();
        // add other maps here.
    }
}