code: public static <Param> PathParamSerializer<Set<Param>> set(String name,
                                                                Function<PSequence<String>, Param> deserialize,
                                                                Function<Param, PSequence<String>> serialize) {
  
          return new NamedPathParamSerializer<Set<Param>>("Set(" + name + ")") {
              @Override
              public PSequence<String> serialize(Set<Param> parameter) {
                  Set<String> serializedParams =
                      serializeCollection(parameter, serialize)
                          .collect(Collectors.toSet());
                  return TreePVector.from(serializedParams);
              }
  
              @Override
              public Set<Param> deserialize(PSequence<String> parameters) {
                  return deserializeCollection(parameters, deserialize).collect(Collectors.toSet());
              }
          };
      }
docs: Create a PathParamSerializer for Set parameters.