I am playing with Google Photos API Explorer. Documentation says that pageToken field in response Populated if there are more albums to retrieve for this request. But in practice it's always populated, even if it's a last page and the next page (using provided token) will return {}.
And because of this bug (feature?) Google Photos API, pageSize Parameter not returning expected results -- I can't detect the real last page without querying next (empty) page (because we can't rely on number of returned albums on current page).
So the question is how to recognize the last page without query to the empty one?