error "Value cannot be null." in MVC with EntityFramework

error shown "Value cannot be null." on line 15. please resolve it.
My code is :- 
EmployeeContext employeeContext = new EmployeeContext(); Line 15: Employee employee = employeeContext.Employee.Single(emp => emp.EmployeeId == id); Line 16: return View(employee); and in global file i using this code : -
Database.SetInitializer<ASP_MVC_1.Models.EmployeeContext>(null);