change song choice to mandatory

booking.regn_form.inc

@@ -916,7 +916,7 @@ function booking_form($node, &$form_state, $inserting = FALSE, $early_access_all
       '#type' => 'textfield',
       '#title' => t("Let us know if there's a song you'd love to sing during the week."),
       '#maxlength' => 200,
-      '#required' => FALSE,
+      '#required' => TRUE,
       '#default_value' => !empty($data->booking_song_choice) ? $data->booking_song_choice : ''
     );
   }