/**
  * @param SnakList $qualifiers
  * @param Summary|null $summary
  *
  * @throws ChangeOpException
  */
 protected function removeQualifier(SnakList $qualifiers, Summary $summary = null)
 {
     if (!$qualifiers->hasSnakHash($this->snakHash)) {
         throw new ChangeOpException("Qualifier with hash {$this->snakHash} does not exist");
     }
     $removedQualifier = $qualifiers->getSnak($this->snakHash);
     $qualifiers->removeSnakHash($this->snakHash);
     $this->updateSummary($summary, 'remove', '', $this->getSnakSummaryArgs($removedQualifier));
 }