code: public void dropIndex(final DBObject index) {
          try {
              executor.execute(new DropIndexOperation(getNamespace(), wrap(index), getWriteConcern()), getReadConcern());
          } catch (MongoWriteConcernException e) {
              throw createWriteConcernException(e);
          }
      }
docs: Drops an index from this collection.  The DBObject index parameter must match the specification of the index to drop, i.e. correct
  key name and type must be specified.
  
  @param index the specification of the index to drop
  @throws MongoException if the index does not exist
  @mongodb.driver.manual core/indexes/ Indexes