Entity Framework 6 Code First Fail - entity-framework-6

Question

I'm new in Entity Framework and I'm testing a simple application but it doesn't work.
Let me explain step by setp what I'm doing:
1- Create a Console App using VS 2013 Express
2- Include a reference to EF6 by Nuget
3- Create the Student Class:
namespace CSharp_CodeFirst
{
public class Student
{
public int Id { get; set; }
public string name { get; set; }
public string email { get; set; }
}
}
4- Create the context class
using System.Data.Entity;
namespace CSharp_CodeFirst
{
public class StudentDataContext : DbContext
{
public StudentDataContext() : base()
{
}
public DbSet<Student> Students;
}
}
5- Create the code in Program.cs
namespace CSharp_CodeFirst
{
class Program
{
static void Main(string[] args)
{
using (var ctx = new StudentDataContext())
{
Student stud = new Student() { name = "New Student", email="test#test.com" , Id=1 };
ctx.Students.Add(stud);
ctx.SaveChanges();
}
}
}
}
6- Build without errors
7- When I execute the project I get the error :
An unhandled exception of type 'System.NullReferenceException' occurred in CSharp_CodeFirst.exe
Object reference not set to an instance of an object.
The error occur in this line of code : ctx.Students.Add(stud);
I'm using the sample in this site : http://www.entityframeworktutorial.net/code-first/simple-code-first-example.aspx
I Feel Like I'm Forgetting Something, but What ???
Thanks