How to replace a if-statement?

I have the following

public class OfferService {
    
    @Autowired
    private OfferRepository offerRepository;
    @Autowired
    private ModelMapper modelMapper;
    
    public OfferDto getById(Long id){
        Offer offer = offerRepository.findById(id)
                .orElseThrow(()-> new OfferException());
        if(offer.getFim().isAfter(LocalDate.now()))
        {
            return modelMapper.map(offer, OfferDto.class);
        }
        return null;
    }
    
}

So I would like to know how to create a class/interface, so I would replace that if-condition with something else. In fact, I would like to create a class that I could put all my if-statements and conditions.