I would say returning the current page would be confusing. I would be fine with an exception or returning null as both can be handled pretty easily by a dev. I would say an exception may be more useful since it will tell the dev exactly what was wrong instead of their app choking in a null return but I am open to both.

For offset > totalNbPages :

- throwing an exception ?

- returning null ?

- returning last page ?

I would say same as above. Returning last page may be confusing but others are acceptable with a preference toward an exception.