docs: public Set<String> getKeySet() {
          HashSet<String> result = new HashSet<>();
  
          for (PollingDynamicConfig config : children) {
              Iterator<String> iter = config.getKeys();
              while (iter.hasNext()) {
                  String key = iter.next();
                  result.add(key);
              }
          }
  
          return result;
      }