issue: singular vs plural

[MelSumner]

From the README, in Step 2 - I've omitted everything but the relevant parts.

const contentsJson = new StaticSiteJson('content', {
  contentFolder: 'contents',
});

Note: we need to add the contentFolder: 'contents' config because ember-data expects the folder name to be pluralized and broccoli-static-site-json does not do this by default.

Now, when I do this, I get this error:
Directory not found: app-name/content

I can confirm that the folder contents does exist and is in the app's root directory (and not in the app folder or anything else).
I'm not sure how to resolve the issue where it's looking for a singular-form folder instead of the pluralized one? Any advice?