code: @Nullable
      public DBObject findOne(final Object id, final DBObject projection) {
          return findOne(new BasicDBObject("_id", id), new DBCollectionFindOptions().projection(projection));
      }
docs: Get a single document from collection by '_id'.
  
  @param id         value of '_id' field of a document we are looking for
  @param projection specifies which projection MongoDB will return from the documents in the result set.
  @return A document that satisfies the query specified as the argument to this method.
  @mongodb.driver.manual tutorial/query-documents/ Querying