code: public FormMappingOption filterRequestParameterMap(Function<Map<String, Object>, Map<String, Object>> requestParameterMapFilter) {
          if (requestParameterMapFilter == null) {
              throw new IllegalArgumentException("The argument 'requestParameterMapFilter' should not be null.");
          }
          this.requestParameterMapFilter = OptionalThing.of(requestParameterMapFilter);
          return this;
      }
docs: -------------