/**
  * Retrieve the extra indexes for our searchable namespaces, if any
  * exist. If they do exist, also add our wiki to our notFilters so
  * we can filter out duplicates properly.
  *
  * @return string[]
  */
 protected function getAndFilterExtraIndexes()
 {
     if ($this->limitSearchToLocalWiki) {
         return array();
     }
     $extraIndexes = OtherIndexes::getExtraIndexesForNamespaces($this->namespaces);
     if ($extraIndexes) {
         $this->notFilters[] = new \Elastica\Filter\Term(array('local_sites_with_dupe' => $this->indexBaseName));
     }
     return $extraIndexes;
 }