How to handle null IEnumerable (Misconfiguration)

[cristianUrbina]

Hello!! thanks for taking the time to check this out.

This is my mapper:

    [Mapper(
        EnumMappingStrategy = EnumMappingStrategy.ByName,
        UseReferenceHandling = true,
        ThrowOnMappingNullMismatch = false,
        ThrowOnPropertyMappingNullMismatch = false
        )]
    public static partial class FirstTestDtoMapper
    {
        [MapProperty(nameof(FirstTest.Age), nameof(FirstTestDto.CurrentAge))]
        public static partial FirstTestDto FirstTestToDto(FirstTest firstTest);
        public static partial PersonDto PersonToDto(Person person);
    }

And this is the test that is not passing because a null IEnumerable (the children list):

[Fact]
        public void FirstTestDtoMapper_PlainPerson_ShouldBeEqual()
        {
            // arrange
            var person = new Person()
            {
                SSN = 4,
                Name = "Josefina",
            };

            // act
            PersonDto dto = FirstTestDtoMapper.PersonToDto(person);

            // assert
            Assert.NotNull(dto);
            Assert.Equal(person.SSN, dto.SSN);
            Assert.Equal(person.Name, dto.Name);
        }

public class Person
    {
        public int SSN { get; set; }
        public string Name { get; set; }
        public IEnumerable<Person> Children { get; set; }
        public Person Father { get; set; }
        public Person Mother { get; set; }
        public Person FavoritePerson { get; set; }
    }

The workaround I can think of is performing some checking and cleaning using this https://mapperly.riok.app/docs/configuration/before-after-map. Is there a way to handle this without adding any Before / after map code?
I have already tried using Mapper attributes (those you see in the mapper class code).
Thanks again

[TimothyMakkison]

Hey, thanks for using Mapperly.

Do you have nullable reference types enabled?
Looking at the generated code it looks like mapperly doesn't expect the value Children to be nullable (because nullable reference types is enabled). Because of this it doesn't add a null check to Children,resulting in Select throwing an error.

I think you can resolve this issue by annotating your properties like so:

public class Person
{
        public int SSN { get; set; }
        public string Name { get; set; }
        public IEnumerable<Person?>? Children { get; set; }
        public Person? Father { get; set; }
        public Person? Mother { get; set; }
        public Person? FavoritePerson { get; set; }
}

I wouldn't recommend this but adding #nullable disable before Person and PersonDto will disable nullable reference types, letting mapperly treat each property as a potential null value.