private void CreateNewDepartment()
{
    /*Serg's Way - It works */
    /*if ((textBox1.Text != String.Empty) && (comboBox1.SelectedIndex >= 0))
    {
        DepartmentRepository departmentRepo = new DepartmentRepository();
        Person user = new Person()
        {
            Name = ((Person)comboBox1.SelectedItem).Name
        };

        Department department = new Department()
        {
            Name = textBox1.Text,
            Person = user,
        };
        departmentRepo.Add(department);
        departmentRepo.Save();
    }     */

    /*Works also! */
    if ((textBox1.Text != String.Empty) && (comboBox1.SelectedIndex >= 0))
    {
        Person person = (Person)comboBox1.SelectedItem;
        Department department = new Department();
        department.Name = textBox1.Text;
        person.Departments.Add(department);

        peopleRepo.Save();
    }
}