docs: public static Set<Field> getDeclaredFields(Class<?> clazz, FieldFilter filter) {
          Set<Field> fields = new HashSet<Field>();
          Field[] allFields = clazz.getDeclaredFields();
          for(Field field : allFields) {
              if(filter.passFilter(field)) {
                  fields.add(field);
              }
          }
          return fields;
      }