code: public static Mapping<BigDecimal> bigDecimal(Constraint... constraints) {
          return new FieldMapping(
                  InputMode.SINGLE,
                  mkSimpleConverter(s ->
                      isEmptyStr(s) ? BigDecimal.ZERO : new BigDecimal(s)
                  ), new MappingMeta(MAPPING_BIG_DECIMAL, BigDecimal.class)
              ).constraint(checking(BigDecimal::new, "error.bigdecimal", true))
                  .constraint(constraints);
          }
docs: (convert to BigDecimal) mapping
  @param constraints constraints
  @return new created mapping