docs: protected <X> Specification<ENTITY> buildSpecification(Filter<X> filter, Function<Root<ENTITY>, Expression<X>> metaclassFunction) {
          if (filter.getEquals() != null) {
              return equalsSpecification(metaclassFunction, filter.getEquals());
          } else if (filter.getIn() != null) {
              return valueIn(metaclassFunction, filter.getIn());
          } else if (filter.getSpecified() != null) {
              return byFieldSpecified(metaclassFunction, filter.getSpecified());
          }
          return null;
      }