Assumption of string when string or array can be returned from: $obj->getUserEmailAddresses($userID);

I've seen this in a couple of places where a line line this:

public function notify(MaestroNotification &$obj) {
  # ...
  # ...
  # ...
  $to = $obj->getUserEmailAddresses($userID);

is followed by something like this:

  $params = array('message' => $obj->getMessage(), 'subject' => $obj->getSubject(), 'queueID' => $obj->getQueueId());
  $result   = drupal_mail('maestro', $obj->getNotificationType(), $to, language_default(), $params, $from, $send);

The problem is that in the rare case where there is more than one email address an array gets returned when the code is written to only handle a string. Now the issue is probably deeper than that because what I am looking at right now is an empty array however I suspect that is a different issue that is bringing this issue to light by way of cascading.