Nullable Class as a Property is not Nullable. Why? - .net-6.0

Question

I have a class that I created where a property is another class I wrote. I am being warned that my property is non-nullable and I don't understand why. Aren't all properties of nullable classes nullable?
public class Yeast
{
public int? Id { get; set; }
public Code Brand { get; set; }
public Code Style { get; set; }
public string? Trademark { get; set; }
public int? TempMin { get; set; }
public int? TempMax { get; set; }
public double? Alcohol { get; set; }
public string? Note { get; set; }
}
/// <inheritdoc cref="ICode"/>
public class Code : ICode
{
/// <inheritdoc cref="ICode.Id"/>
public int? Id { get; set; }
/// <inheritdoc cref="ICode.ParentId"/>
public int? ParentId { get; set; }
/// <inheritdoc cref="ICode.Literal"/>
public string? Literal { get; set; }
/// <inheritdoc cref="ICode.Enabled"/>
public bool? Enabled { get; set; }
/// <inheritdoc cref="ICode.Description"/>
public string? Description { get; set; }
}
public interface ICode
{
/// <summary>
/// Code Unique Identifier
/// </summary>
int? Id { get; set; }
/// <summary>
/// Code Foreign Key
/// </summary>
/// <remarks>Optional</remarks>
int? ParentId { get; set; }
/// <summary>
/// Literal Name of Code
/// </summary>
string? Literal { get; set; }
/// <summary>
/// Description of Code
/// </summary>
string? Description { get; set; }
/// <summary>
/// Enabled for Use
/// </summary>
bool? Enabled { get; set; }
}

Answer 1

The issue here is that if you do new Yeast().Brand.Id you'll get a NullReferenceException because Brand is null - but you declared it wouldn't be.
So either the constructor needs to set Brand to a non-null Code value, or you need to mark it as nullable so the compiler can flag it in the consuming code (i.e. say that new Yeast().Brand needs to handle the possibility of a null value).