code: public List<String> getList(String key) {
  
      List<String> list = this.parameters.get(key);
      if (list == null) {
        list = Collections.emptyList();
      }
      return list;
    }
docs: Gets the {@link List} of all value for the parameter with with the given <code>key</code>. In general you should
  avoid multi-valued parameters (e.g. http://host/path?query=a&query=b). The JAX-RS API supports this exotic case as
  first citizen so we expose it here but only use it if you know exactly what you are doing.
  
  @param key is the {@link java.util.Map#get(Object) key} of the parameter to get.
  @return the {@link List} with all values of the requested parameter. Will be an {@link Collections#emptyList()
  empty list} if the parameter is not present.