docs: public synchronized boolean migrate(File dir, @CheckForNull File jenkinsHome) {
          if (load(dir)) {
              LOGGER.log(FINER, "migration already performed for {0}", dir);
              return false;
          }
          if (!dir.isDirectory()) {
              LOGGER.log(/* normal during Job.movedTo */FINE, "{0} was unexpectedly missing", dir);
              return false;
          }
          LOGGER.log(INFO, "Migrating build records in {0}", dir);
          doMigrate(dir);
          save(dir);
          if (jenkinsHome != null && offeredToUnmigrate.add(jenkinsHome))
              LOGGER.log(WARNING, "Build record migration (https://jenkins.io/redirect/build-record-migration) is one-way. If you need to downgrade Jenkins, run: {0}", getUnmigrationCommandLine(jenkinsHome));
          return true;
      }