Apollo-tooling: Improve error messages if the service is not published

[lnmunhoz]

Summary

I was setting up my schema in the Graph Manager for first time, and I tried to run apollo service:check command before running apollo service:push to see what happens.

Intended outcome:
I was expecting some error message saying No services publishet yet or No graph found and instructions to follow up.

Actual outcome:
I got the following error:

 ✔ Loading Apollo Project
  ✔ Loading Apollo Project
  ✖ Validating schema against tag current on graph <graph-id>
    → Cannot read property 'hash' of null
    Comparing schema changes
    Reporting result
Error: Cannot read property 'hash' of null
    at execute.then (~/path/to/node_modules/apollo-language-server/lib/engine/index.js:63:23)
error Command failed with exit code 2.

Then, I published using apollo service:push, and tried again. Everything worked as expected.

It's not a primary issue, but the developer experience could be better since I am setting up things for the first time and the cli didn't helped me to troubleshoot.

How to reproduce the issue:
Run apollo service:check with an ENGINE_API_KEY of a new service that is not puslished yet.

Versions
node: 10.16.3
apollo: 2.18.3
graphql: 14.5.8

[JakeDawkins]

Oof. yeah, this is a really bad error. thanks for pointing that out! I'll take a look at fixing that soon :)