When can a null check throw a NullReferenceException

in C# you can overload operators to add custom logic on some comparison like this. For example:

class Test
{
    public string SomeProp { get; set; }
    
    public static bool operator ==(Test test1, Test test2)
    {
        return test1.SomeProp == test2.SomeProp;
    }

    public static bool operator !=(Test test1, Test test2)
    {
        return !(test1 == test2);
    }
}

then this would produce a null reference exception:

Test test1 = null;
bool x = test1 == null;