The correct way to validate and close a modal form

winforms_modal_form_good.cs

private void btnOK_Click(object sender, EventArgs e)  
{
    if (Validate())
    {
        _selectedUsers.Clear();

        foreach (var user in _allUsers.Where(u => u.Selected))
            _selectedUsers.Add(user.UserId, user.UserName);
    }
    else
        DialogResult = DialogResult.None;
}