Interests saved as `null` if no values provided. Should save as []

[brettski]

Describe the bug
When a member creates or updates their profile and they don't include interests (members.interests), the record is written back to the database with a value of null. members.interests is an array, and should be [] when no values are set, not null.

[saragibby]

Marking this as internal staff as without the ability for external contributors to authenticate in local development environment we are unable to access the edit profile page and replicate the issue to fix.