code: public void addValues(String name, List<V> values) {
          List<V> lo = get(name);
          if (lo == null) {
              lo = new ArrayList<>();
          }
          lo.addAll(values);
          put(name, lo);
      }
docs: Add values to multi valued entry. If the entry is single valued, it is
  converted to the first value of a multi valued entry.
  
  @param name   The entry key.
  @param values The List of multiple values.