Determine if a property is nullable reliably from a Type

In my current project, I need to check, for a given Type, if any of its properties is nullable. Nullable reference types is enabled in this solution so I want the result to show the property is nullable where the ? is appended to the type name.

Let’s say we have some sample classes like these

    public enum Genre
    {
        Drama,
        Comedy,
        Horror
    }

    public class Studio
    {
        public string Name { get; set; }
    }

    public class Director
    {
        public string Name { get; set; }
    }

    public class Movie
    {
        public string Title { get; set; }
        public string? Description { get; set; }

        public Genre Genre { get; set; }
        public Genre? SubGenre { get; set; }

        public DateTime ProductionDate { get; set; }
        public DateTime? ReleaseDate { get; set; }

        public Director Director { get; set; }
        public Studio? Studio { get; set; }

        public int DaysInProduction { get; set; }
        public int? NumberOfStaff { get; set; }
    }

I thought there should be a simple solution to this as it is not uncommon to know if a property is nullable. One of the most common answers is using Nullable.GetUnderlyingType. However the result is not what I expect.

var type = typeof(Movie);

foreach (var property in type.GetProperties())
{
    var isNullable = Nullable.GetUnderlyingType(property.PropertyType) != null;

    Console.WriteLine($"Property {property.Name} is {(isNullable ? "nullable" : "not nullable")}");
}

When the property type is a reference, this solution always results in not nullable – string, Director and Studio.

Another common answer is to check if it’s a generic type and if its generic type is of Nullable<>

var type = typeof(Movie);

foreach (var property in type.GetProperties())
{
    var isNullable = property.PropertyType.IsGenericType &&
                     property.PropertyType.GetGenericTypeDefinition() == typeof(Nullable<>);

    Console.WriteLine($"Property {property.Name} is {(isNullable ? "nullable" : "not nullable")}");
}

This also returns the same result as the previous solution.

After spending a bit more time researching a more reliable solution, I come across NullabilityInfoContext which was introduced in .NET 6. This solution returns the result I expect.

var nullabilityContext = new NullabilityInfoContext();
var type = typeof(Movie);

foreach (var property in type.GetProperties())
{
    var nullabilityInfo = nullabilityContext.Create(property);

    var isNullable = nullabilityInfo.WriteState == NullabilityState.Nullable;

    Console.WriteLine($"Property {property.Name} is {(isNullable ? "nullable" : "not nullable")}");
}