AmpDocumentNetworkFirst.makeRequest return is not nullable but method body implies that it might be nullable

inside the body of `makeRequest` in the `AmpDocumentNetworkFirst` class there is a check for `request` where it could be nullable but we return `request` anyways as the base case and don't state it in the method signature return type.

question really is, does calling `makeRequest` return something that is nullable from the `NetworkFirst` implementation in workbox?

Start by reading AmpDocumentNetworkFirst.makeRequest and tracing the corresponding NetworkFirst implementation in Workbox. Compare the possible return value with the declared method signature, then confirm the signature and behavior agree and add or update coverage if the repository provides a relevant test.

Written by the indexing model from the issue text.