response will be undefined for 404 endpoint

https://github.com/github-tools/github/blob/24223f7a51ba935f1c86ffd552dac20e8f3e359d/lib/Requestable.js#L187

In the above code **response** will be undefined if the request is for a non-existing endpoint (which will result in 404 response).

In-order to re-produce invoke getSha() method for a non-existing in the repository

Read lib/Requestable.js at line 187, then reproduce the issue by invoking getSha() for a nonexistent endpoint in the repository. Confirm the 404 path no longer leaves response undefined and verify the relevant behavior with the project's existing tests.

Written by the indexing model from the issue text.