How to fix Java 9 Optional "Cannot return a void result" error message?

I had a class with a method like this:

public class Client {
    
private project.enums.ClientType clientType;

private ClientType clientTypeV2;


    @JsonIgnore
    public Optional<Integer> getCodeClientTypeV2() {
        
        return Optional.ofNullable(this.clientTypeV2).map(ClientType::getCode);
    }

}

But I would like to change the logic of this method. I want that if clientTypeV2 is filled, it returns the code for that object. Otherwise, I want it to return the code that is in the enum of the clientType. How to do this using java 8? I tried the following code but an error message appears "Cannot return a void result"

@JsonIgnore
public Optional<Integer> getCodeClientTypeV2() {

 return Optional.ofNullable(this.clientTypeV2).ifPresentOrElse(ClientType::getCode, () -> this.clientType.getCode());
}

#Edit 1

I tried this:

@JsonIgnore
public Integer getCodeClientTypeV2() {

return Optional.ofNullable(this.clientTypeV2)
.map(ClientType::getCode)
.orElse(this.clientType.getCode()) ;

}

In debug, although clientTypeV2 is filled, the execution flow is entering inside orElse and giving NullPointerException because the clientType is null. What am I missing?

There are different solutions, depending on whether getCode can return null.

When you don’t want the alternative expression to be evaluated beforehand, you have to use orElseGet(Supplier<? extends T> other) instead of orElse(T other).

return Optional.ofNullable(clientTypeV2).map(ClientType::getCode)
    .orElseGet(() -> clientType.getCode());

If getCode can not return null and you only want to deal with the possibility that either clientTypeV2 or clientType can be null, you can also use

return Optional.ofNullable(clientTypeV2).orElse(clientType).getCode();

or even simpler

return (clientTypeV2 != null? clientTypeV2: clientType).getCode()

Common to all solution is the assumption that at least on of clientTypeV2 or clientType is not null.

By convention, if you are using orElse, you are returning a constant, guaranteed present value. orElse either unwraps the value contained in the Optional, or uses the default value you provide instead.

If you don't want to change the method signature, use Optional#or instead. You will have to be intelligent about null checks for your clientType object, since if it doesn't exist, you can't rely on it being a concrete returnable thing.

return Optional.ofNullable(this.clientTypeV2)
               .map(ClientType::getCode)
               .or(this.clientType.getCode());