This check was a leftover from the resumeKey pagination, where empty responses are supposed to be impossible. With the page pagination, they are possible.

The proper way to do that (with asyncio) is of course aiohttp. A major drawback of the implemented approach is that running tasks can't be cancelled in case of an error. However, it works with just the standard library, and that advantage outweighs the awkward error handling for now.

resumeKey pagination is horribly broken. It may return incomplete results or infinite loops.