docs: def ChunksExist(self, chunk_numbers):
      """Do we have this chunk in the index?"""
      index_urns = {
          self.urn.Add(self.CHUNK_ID_TEMPLATE % chunk_number): chunk_number
          for chunk_number in chunk_numbers
      }
  
      res = {chunk_number: False for chunk_number in chunk_numbers}
  
      for metadata in aff4.FACTORY.Stat(index_urns):
        res[index_urns[metadata["urn"]]] = True
  
      return res