public department GetDepartment(string postalCode)
{
var dptCode = GetDptCode(postalCode);
var departement = (Departments.Contains(dptCode)) ? Departments[dptCode] : null;
return(departement);
}
private bool HasDepartment(Department dep)
{
if (dep == null)
{
throw new ArgumentNullException();
}
return(Departments.Contains(dep));
}