code: @Nullable
      public DBObject findOne(@Nullable final DBObject query, final DBCollectionFindOptions findOptions) {
          return find(query, findOptions).one();
      }
docs: Get a single document from collection.
  
  @param query          the selection criteria using query operators.
  @param findOptions    the options for the find operation.
  @return A document that satisfies the query specified as the argument to this method.
  @mongodb.driver.manual tutorial/query-documents/ Querying
  @since 3.4