requests and remove a common source of non-null assertions (`!!`) on the response body.

The alpha releases in the 5.0.0 series have production-quality code and an unstable API. We expect
to make changes to the APIs introduced in 5.0.0-alpha.X. These releases are safe for production use
and 'alpha' strictly signals that we're still experimenting with some new APIs. If you're eager for
the fixes or features below, please upgrade.