code: public String[] replaceParameter(String name, String value)
    {
      Map<String, String[]> map = getMap();
      String[] v = map.put(name, new String[] { value });
      rebuildQuery();
      return v;
    }
docs: Replace existing or add new parameter with given
  value. Any existing parameter values are
  deleted prior to adding the new value.
  
  @param name parameter to replace
  @return previous values or null if parameter doesn't exist