Warning: Invalid argument supplied for foreach()

Hello,

I have some code which gives me the 'Warning: Invalid argument supplied for foreach()' error.

$groups = "";
foreach ($vbulletin->GPC['user']['membergroupids'] AS $key => $val){
$groups .= "{$val},";
}

I get the error only when I don't select an additional membergroup for a specific user I'm editing in the Admin CP. When I select an additional membergroup for a user, though, it works without displaying an error.

Basically, the problem is how to make this code so if an additional membergroup is NOT selected when updating a user, I won't see the 'Warning: Invalid argument supplied for foreach()' error.

If anyone knows how to fix this, I'd really appreciate it.

Thanks!

if (is_array($vbulletin->GPC['user']['membergroupids']) {
  foreach ($vbulletin->GPC['user']['membergroupids'] AS $key => $val){
    $groups .= "{$val},";
  }
}