code: public CompletableFuture<Version> addNewEntryIfAbsent(String tableName, String key, @NonNull byte[] value) {
          // if entry exists, we will get write conflict in attempting to create it again. 
          return expectingDataExists(addNewEntry(tableName, key, value), null);
      }
docs: Method to add new entry to table if it does not exist.
  @param tableName tableName
  @param key Key to add
  @param value value to add
  @return CompletableFuture which when completed will have added entry to the table if it did not exist.