Ember-CLI-Mirage enforcing JSON:API?

Stumped on a couple failures and want to know if I'm understanding Mirage correctly:

1.In ember-cli-mirage, am I correct that the server response I define should reflect what my actual server is returning? For example:

this.get('/athletes', function(db, request) {
  let athletes = db.athletes || [];
  return {
    athletes: athletes,
    meta: { count: athletes.length }
  }
});

I am using custom serializers and the above matches the format of my server response for a get request on this route, however, on two tests I'm getting two failures with this error: normalizeResponse must return a valid JSON API document: meta must be an object

2.Is mirage enforcing the json:api format, and is it doing so because of the way I'm setting up the tests?

For example, I have several tests that visit the above /athletes route, yet my failures occur when I use an async call like below. I would love to know the appropriate way to correctly overwrite the server response behavior, as well as why the normalizeResponse error appears in the console for 2 tests but only causes the one below to fail.

test('contact params not sent with request after clicking .showglobal', function(assert) {
  assert.expect(2);
  let done = assert.async();
  server.createList('athlete', 10);

  //perform a search, which shows all 10 athletes
  visit('/athletes');
  fillIn('.search-inner input', "c");

  andThen(() => {
    server.get('/athletes', (db, request) => {
      assert.notOk(params.hasOwnProperty("contacts"));
      done();
    });

    //get global athletes, which I thought would now be intercepted by the server.get call defined within the andThen block
    click('button.showglobal');
  });
});

Result:

✘ Error: Assertion Failed: normalizeResponse must return a valid JSON API document:
    * meta must be an object
         expected true

I tried changing my server response to a json:api format as suggested in the last example here but this looks nothing like my actual server response and causes my tests to fail since my app doesn't parse a payload with this structure. Any tips or advice must appreciated.