code: public static Mapping<Double> doublev(Constraint... constraints) {
          return new FieldMapping(
                  InputMode.SINGLE,
                  mkSimpleConverter(s ->
                      isEmptyStr(s) ? 0.0d : Double.parseDouble(s)
                  ), new MappingMeta(MAPPING_DOUBLE, Double.class)
              ).constraint(checking(Double::parseDouble, "error.double", true))
                  .constraint(constraints);
          }
docs: (convert to Double) mapping
  @param constraints constraints
  @return new created mapping