code: public void dropIndex(final String indexName) {
          try {
              executor.execute(new DropIndexOperation(getNamespace(), indexName, getWriteConcern()), getReadConcern());
          } catch (MongoWriteConcernException e) {
              throw createWriteConcernException(e);
          }
      }
docs: Drops the index with the given name from this collection.
  
  @param indexName name of index to drop
  @throws MongoException if the index does not exist
  @mongodb.driver.manual core/indexes/ Indexes