private function addMissingParentGroups($groupName)
{
$parent = '';
foreach (explode('\\', $groupName) as $part) {
$parent = ltrim($parent . '\\' . $part, '\\');
if (!isset($this->lowercasedGroupNames[strtolower($parent)])) {
$this->groups[$parent] = $this->elements->getEmptyList();
}
}
}