Optional method implementation in an abstract class

I'm working on some framework and I got an abstract class, which should be implemented.

Now I got some other stuff the user should be able to configure, but it is optional.

So instead of the abstract method:

public abstract class AbstractModule {    public void doSomething() {        if (logMessage() != null)            System.out.println(logMessage());        doStuff();    }    protected abstract String logMessage(); // I'm optional    protected abstract void doStuff();}

I thought of just checking for an interface implementation:

public interface Log {    String logMessage();}public abstract class AbstractModule {    public void doSomething() {        if (this instanceof Log) {            if (((Log) this).logMessage() != null)                System.out.println(((Log) this).logMessage());        }        doStuff();    }    protected abstract void doStuff();}

So, if someone is implementing AbstractModule with the interface Log it would also show the message. The benefit for the implementer that I see: She doesn't need to care about implementing logMessage(), as it would be in the first example. Is this a valid approach or should it be done differently?

Thanks in advance!

Best regards