Complete Test Coverage

Hello @benbjohnson , I recently came across your article while trying to learn about how to test HTTP packages in Golang, and I think what you did was amazing.

### What I found out

However, the test file content you provided was not fully testing all the scenarios in the function, as I ran the tests and it recorded an `83.3%` coverage of the statements.

### What I did

- I then proceeded to try to generate the coverage file, and just as I suspected, the statement that had not been tested was the `return nil` part.

- I added the test scenario, and now we have a complete `100%` coverage on the test.

### Conclusion

- As I have seen some issues have been created and have stayed open for about half a decade now, I would like to know if it is still being maintained, to add my Pull request to the repository.