code: public void merge(RunResults runResults) {
          for (RootMethodRunResult srcResult : runResults.rootMethodRunResults) {
              if (getRunResultByRootMethodKey(srcResult.getRootMethodKey()) != null) {
                  throw new RuntimeException(String.format(
                          "not supported: root method %s is called multi times", srcResult.getRootMethodKey()));
              }
              addRootMethodRunResults(srcResult);
          }
      }
docs: (since merging can break correct reference)