why i dont get exception ?

class First
    {
        string name;
        public string Name
        {
            get { return name; }
            set { name = value; }
        }
        public First(string _name)
        {
            
            name = _name;
        }
        public override int GetHashCode()
        {
            return name.GetHashCode();
        }
    }
    class Second
    {
        int id;
        public int Id
        {
            get { return id; }
            set { id = value; }
        }
        public Second(int _id)
        {
            id = _id;
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            First obj1 = new First("mohamed");
            First obj2 = new First("Ali");
            Second Nobj = new Second(1);
            Hashtable ht = new Hashtable();
            ht[obj1] = Nobj;
            ht[obj2]=Nobj;
            ht.Add(new First("mohamed"), Nobj);           
        }
    }