code: public static <T> Mapping<List<T>> list(Mapping<T> base, Constraint... constraints) {
          String mname = "list of " + base.meta().name;
          return new FieldMapping<>(
                  InputMode.MULTIPLE,
                  ((name, data) -> {
                      logger.debug("list - converting {}", name);
  
                      return indexes(name, data).stream()
                              .map(i -> base.convert(name + "[" + i + "]", data))
                              .collect(Collectors.toList());
                  }),
                  ((name, data, messages, options) -> {
                      logger.debug("list - validating {}", name);
  
                      return indexes(name, data).stream()
                              .flatMap(i -> base.validate(name + "[" + i + "]", data, messages, options).stream())
                              .collect(Collectors.toList());
                  }), new MappingMeta(mname, List.class, base)
              ).constraint(constraints);
          }
docs: (mapping) convert to list of values
  @param base base mapping
  @param constraints constraints
  @param <T> base type
  @return new created mapping