@Override
            public R next() {
                return mapper.apply(getDelegate().next());
            }
Returns a {@code ResultIterable<U>} derived from this {@code ResultIterable<T>}, by
transforming elements using the given mapper function.

@param mapper function to apply to elements of this ResultIterable
@param <R>    Element type of the returned ResultIterable
@return the new ResultIterable
core/src/main/java/org/jdbi/v3/core/result/ResultIterable.java