code: public void remove(final ObjectId id) {
          if (id == null) {
              throw new IllegalArgumentException("file id can not be null");
          }
  
          filesCollection.remove(new BasicDBObject("_id", id));
          chunksCollection.remove(new BasicDBObject("files_id", id));
      }
docs: Removes the file matching the given id.
  
  @param id the id of the file to be removed
  @throws com.mongodb.MongoException if the operation fails