If the `size` URL param wasn't present, then `size=null` would be passed
to `/posts/:id.js`, which would fail because `null` wasn't a valid size.
Regression in 8841de68ac.
If the `size` URL param wasn't present, then `size=null` would be passed
to `/posts/:id.js`, which would fail because `null` wasn't a valid size.
Regression in 8841de68ac.