Docs processing fails silently.

The below appears successful even though it failed to generate any docs. ember-data is locally available, the version matches as expected, and the docs file is generated at data/packages/-ember-data/dist/docs/data.json as expected.

```cli
yarn gen --project ember-data --version 3.28.0 ~/github/oss/ember-jsonapi-docs  master
yarn run v1.22.5
$ node -r esm generate-local.js --project ember-data --version 3.28.0
Running 'yarn'
[1/5] Validating package.json...
[2/5] Resolving packages...
success Already up-to-date.

Running 'yarn workspace ember-data docs'
$ mkdir -p dist && ember ember-cli-yuidoc
info: Scanning for yuidoc.json file.
info: Loading package.json data from: /Users/runspired/github/oss/data/packages/-ember-data/package.json
info: Loading yuidoc.json data from: /Users/runspired/github/oss/data/packages/-ember-data/yuidoc.json
info: YUIDoc Starting from: ../adapter/addon,../canary-features/addon,../debug/addon,../model/addon,../private-build-infra/addon,../record-data/addon,../serializer/addon,../store/addon,addon
Filtering tags...
Skipping items with the tags: internal
info: Making out dir: dist/docs
info: Parsed 144 files in 0.096 seconds
info: Building..
info: Compiling Templates
info: Making default directories: classes,elements,modules,files
info: Copying Assets
info: Rendering and writing 14 modules pages.
info: Loading theme from /Users/runspired/github/oss/data/node_modules/yuidocjs/themes/default/theme.json
info: Preparing index.html
info: Writing API Meta Data
info: Writing index.html
info: Finished writing module files
info: Rendering and writing 51 class pages.
info: Rendering and writing 0 class pages.
info: Finished writing element files
info: Rendering and writing 82 source files.
info: Finished writing class files
info: Rendering and writing 82 source files.
info: Finished writing source files
info: Finished writing source files
info: Finished writing 230 files in 0.864 seconds

$ node index.js --project ember-data --version 3.28.0 --ignorePreviouslyIndexedDoc --no-sync
Skipping downloading docs
tmp/json-docs/ember-data/projects/ember-data.json false
Starting to process ember-data-3.28.0
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.
```