code: private CompletableFuture<PageWrapper> locateNextPage(TimeoutTimer timer) {
          if (this.lastPage.get() == null) {
              // This is our very first invocation. Find the page containing the first key.
              return this.locatePage.apply(this.firstKey, this.pageCollection, timer);
          } else {
              // We already have a pointer to a page; find next page.
              return getNextLeafPage(timer);
          }
      }
docs: region Helpers