code: public static String getPropertyNameForBranch(String key, int numBranches, int branchId) {
      Preconditions.checkArgument(numBranches >= 0, "The number of branches is expected to be non-negative");
      Preconditions.checkArgument(branchId >= 0, "The branchId is expected to be non-negative");
      return numBranches > 1 ? key + "." + branchId : key;
    }
docs: Get a new property key from an original one with branch index (if applicable).
  
  @param key      property key
  @param numBranches number of branches (non-negative)
  @param branchId    branch id (non-negative)
  @return a new property key