When using Ninjects ConstructorArgument you can specify the exact value to inject to specific parameters. Why can't this value be null, or how can I make it work? Maybe it's not something you'd like to do, but I want to use it in my unit tests.. Example:

public class Ninja
{
    private readonly IWeapon _weapon;
    public Ninja(IWeapon weapon)
    {
        _weapon = weapon;
    }
}

public void SomeFunction()
{
    var kernel = new StandardKernel();
    var ninja = kernel.Get<Ninja>(new ConstructorArgument("weapon", null));
}