Hide categories select box when only one category is defined and default

Hi,
Here is a suggestion to reduce the 'complexity' of the user interface. When only one category is defined and it is set as the default (selected), the user does not need to see the select box for the categories when sending a mass contact message (since there is nothing to choose from).
Here is my proposal code for lines 552-559 in mass_contact.module, to hide the categories selection in this case:

function mass_contact_mail_page() {
/* [...] */
    if ((count($categories) > 1) || !isset($default_category)) { // display a choice when one is needed
      $form['cid'] = array(
        '#type'          => 'select',
        '#title'         => t('Category'),
        '#default_value' => $default_category,
        '#options'       => $categories,
        '#required'      => true,
        '#multiple'      => true,
      );
    } else { // otherwise, just use the default category
      $form['cid'] = array(
        '#type'          => 'value',
        '#value'         => array($default_category), // this must be an array, otherwise the code breaks upon submit
      );
    }
/* [...] */
}