Spring Boot: The method add(Converter) in the type Set<Converter> is not applicable for the arguments (...)

Question

When trying to add something to the converters HashSet in ConversionConfig.java, I get the following error in RED:

Error:

The method add(Converter) in the type Set<Converter> is not applicable for the arguments (RoomEntityToReservationResponseConverter)

ConversionConfig.java:

      @Configuration 
        public class ConversionConfig {
        
            @SuppressWarnings("rawtypes")
            private Set<Converter> getConverters() {
                    Set<Converter> converters = new HashSet<Converter>();
                    converters.add(new RoomEntityToReservationResponseConverter());
        
                    return converters;
            }
        
            @Bean public ConversionService conversionService() {
                    ConversionServiceFactoryBean bean = new ConversionServiceFactoryBean();
                    bean.setConverters(getConverters());
                    bean.afterPropertiesSet();
        
                    return bean.getObject();
            }
        }

RoomEntityToReservationResponseConverter.java:

    public class RoomEntityToReservationResponseConverter implements Converter<RoomEntity, ReservationResponse>{
    
        @Override
        public ReservationResponse convert(RoomEntity source) {
            
            ReservationResponse reservationResponse = new ReservationResponse();
            reservationResponse.setRoomNumber(source.getRoomNumber());
            reservationResponse.setPrice( Integer.valueOf(source.getPrice()) );
            
            Links links = new Links();
            Self self = new Self();
            self.setRef(ResourceConstants.ROOM_RESERVATION_V1 + "/" + source.getId());
            links.setSelf(self);
            
            reservationResponse.setLinks(links);
            
            return reservationResponse;
        }
    
        
        
    }

Not sure what is going on - I am new to Spring Boot. Looking at similar questions has not helped, because I don't understand the root problem, if someone could spell out the solution using code from this particular instance, that would be helpful to get a better idea.