code: public static Mapping<Float> floatv(Constraint... constraints) {
          return new FieldMapping(
                  InputMode.SINGLE,
                  mkSimpleConverter(s ->
                      isEmptyStr(s) ? 0.0f : Float.parseFloat(s)
                  ), new MappingMeta(MAPPING_FLOAT, Float.class)
              ).constraint(checking(Float::parseFloat, "error.float", true))
                  .constraint(constraints);
          }
docs: (convert to Float) mapping
  @param constraints constraints
  @return new created mapping