A default constructor that initializes the Courses property to an instance of List<Course>

using System.Collections.Generic; 
namespace Treehouse.CodeChallenges
{
    public class Courses
    {

        public Courses()
        {
            Course = new List<Course>();
        }
        public int Id { get; set; }
        public int  TeacherId {get; set;}
        public string Title { get; set; }
        public string Description { get; set; }
        public int Length { get; set; }
        public  Teacher Teacher { get; set; }
        public ICollection<Courses> Course {get; set; }

    }
}

namespace Treehouse.CodeChallenges
{
    public class Teacher
    {
        public int Id { get; set; }
        public string FirstName { get; set; }
        public string LastName { get; set; }
    }
}