Use a default value for the parameter that will be parsed by JSON.parse

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What does this MR do and why?

This commit aims to prevent unnecessary error logging to the Sentry caused by JSON.parse when the given value is undefined. So I've used a default value for that value.

Closes: #490960 (closed)

Changelog: changed

Screenshots or screen recordings

Before	After
before.mov	after.mov

How to set up and validate locally

1. Run GitLab.
2. Navigare to <project> -> Settings -> Repository
3. Open the developers console (or observe Sentry logs).
4. The JSON.parse error caused by initAccessDropdown() should not be present and logged to the Sentry.