The Hooks view does not display a list of hooks ("No hooks are defined"), despite data being returned from the GraphQL query.

Steps to reproduce the behavior:

1. Go to https://community-tc.services.mozilla.com/api/hooks/v1/hooks. A JSON object is returned showing multiple hook groups.
2. Go to https://community-tc.services.mozilla.com/hooks. The display shows "No hooks are defined".

Expected behavior

The /hooks page should show a list of hook groups, and allow expanding to see hooks within the groups.

Firefox-ci, on 43.2.0, shows the correct behavior: https://firefox-ci-tc.services.mozilla.com/hooks

Taskcluster version

• Works on 43.2.0
• Broken on 44.1.0

Screenshots

Broken version on community-tc:

Working version on firefox-ci:

Additional context

Probably caused by PR #4921, which changed the implementation of the tree view to fix issue #2749.

Found by @pyoor, reported by @Archaeopteryx, possible cause identified by @bhearsum.