docs: private void merge(YamlNode source, YamlNode target) {
          if (source == null) {
              return;
          }
  
          checkAmbiguousConfiguration(source, target);
  
          if (isMapping(source)) {
              mergeMappingNodes(asMapping(source), asMapping(target));
          } else if (isSequence(source)) {
              mergeSequenceNodes(asSequence(source), asSequence(target));
          }
      }