Dog Identify - my solution

using System;

public interface IDog
{
    string Name {get;}
    string Breed {get;}
}

public class Dog: IDog
{
        public string Name {get;}
        public string Breed {get;}

        public Dog(string name, string breed)
        {
                this.Name = name;
                this.Breed = breed;
        }

        public Dog(string breed)
         :this(null,breed)
        {
                this.Breed = breed;
        }

        public Dog()
        {
        }

        public override string ToString()
        {
                string s;

                if(this.Breed != null && this.Name != null)
                {
                   s = string.Format("The {0} dog {1} said BARK!",this.Breed,this.Name);
                }
                else if(this.Name == null && this.Breed != null)
        {
             s = string.Format("The unnamed {0} dog said BARK!",this.Breed);
        }
            else
                {
                     s = null;
                }
                return s;
        }
}

public class Program
{
        public static void Main()
        {

                Dog sharo = new Dog("Sharo","corgi");

                Dog rex = new Dog("Rex","poodle");

                Dog unnamed = new Dog(null,"hound");

        Dog[] dogs = new Dog[]{sharo, rex,unnamed};


            foreach(var dog in dogs)
            {
                Console.WriteLine(dog);
            }
        }
}