Rails -- NoMethodError undefined method unpack1 for nil NilClass

I recently started a new application and tried running the generated tests and got this:

rails test test/models/user_test.rb
Running via Spring preloader in process 27379
Run options: --seed 14413

# Running:

E

Error:
UserTest#test_can_delete_user_with_teams:
NoMethodError: undefined method `unpack1' for nil:NilClass
    app/models/user/connected_account.rb:37:in `<class:ConnectedAccount>'
    app/models/user/connected_account.rb:31:in `<main>'


rails test test/models/user_test.rb:57

E

Error:
UserTest#test_user_has_a_personal_team:
NoMethodError: undefined method `unpack1' for nil:NilClass
    app/models/user/connected_account.rb:37:in `<class:ConnectedAccount>'
    app/models/user/connected_account.rb:31:in `<main>'


rails test test/models/user_test.rb:52

E

Error:
UserTest#test_user_has_many_teams:
NoMethodError: undefined method `unpack1' for nil:NilClass
    app/models/user/connected_account.rb:37:in `<class:ConnectedAccount>'
    app/models/user/connected_account.rb:31:in `<main>'


rails test test/models/user_test.rb:46



Finished in 0.060465s, 49.6155 runs/s, 0.0000 assertions/s.
3 runs, 0 assertions, 0 failures, 3 errors, 0 skips

Now this is the the first time I've used test (as opposed to RSpec) in more than a decade and I was more than a bit taken aback. A quick Stack Overflow led me to:

The error happens if you call Base64.decode64(nil). The method however is strictly expecting a String object here.

Now the line of code in question is:

attr_encrypted :access_token, key: Base64.decode64(Rails.application.credentials.access_token_encryption_key)

So the implication is that:

Rails.application.credentials.access_token_encryption_key

is returning nil.

The solution is actually pretty simple – create the credentials file using:

EDITOR=vi rails credentials:edit --environment test

See this blog post for why you have to use EDITOR=vi.