[bug] JavaScript error on Access credentials add/edit page

[pandafy]

Steps to replicate:

1, Run development server
2. Visit http://localhost/admin/connection/credentials/add/

Thanks to @nemesisdesign for reporting this in #333 (review)

@NoumbissiValere do you have any thoughts regarding the cause of the bug?

[nemesifier]

Thanks for testing on master @pandafy. Looks like it's been introduced in the system defined variables PR.