docs: public static void dumpPlanToFile(String outputDirName, RebalancePlan plan) {
          if(outputDirName != null) {
              File outputDir = new File(outputDirName);
              if(!outputDir.exists()) {
                  Utils.mkdirs(outputDir);
              }
              try {
                  FileUtils.writeStringToFile(new File(outputDirName, "plan.out"), plan.toString());
              } catch(IOException e) {
                  logger.error("IOException during dumpPlanToFile: " + e);
              }
          }
      }