code: private List<Object> convertToObjectKeys(Collection keys) {
          if (keys == null || keys.isEmpty()) {
              return Collections.emptyList();
          }
          final List<Object> objectKeys = new ArrayList<>(keys.size());
          for (Object key : keys) {
              objectKeys.add(toObject(key));
          }
          return objectKeys;
      }
docs: Deserialises all of the items in the provided collection if they
  are not deserialised already.
  
  @param keys the items to be deserialised
  @return the list of deserialised items