Aiohttp error in getaddrinfo()

aiohttp_getaddrinfo_error.py

import aiohttp
import asyncio


async def request(session, url):
    try:
        async with session.get(url) as resp:
            pass
    except:
        # raises: TypeError: getaddrinfo() argument 1 must be string or None
        # after a couple of requests to different hosts
        import pdb; pdb.post_mortem()
        raise SystemExit


async def testit(loop):
    connector = aiohttp.TCPConnector(limit=17, limit_per_host=19, resolver=aiohttp.AsyncResolver(), use_dns_cache=False)
    # session = aiohttp.ClientSession(loop=loop)
    session = aiohttp.ClientSession(loop=loop, connector=connector)
    await asyncio.gather(*[
        request(session, url)
        for _ in range(20)
        for url in ('https://www.facebook.com', 'https://vk.com', 'https://google.com')
    ])


if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    loop.run_until_complete(testit(loop))