ajax helper with no source or target defaults to body

[MichaelWest22]

Description

recent change #2878 has caused the default behavior of the ajax helper function for when no source or target is supplied to change to error on a target error instead of targeting body as it should do by default. The recent fix was put in to handle situations where an invalid source or target were supplied which would previously fall back to targeting body in error but the logic for that fix did not handle the case where nothing is supplied for source or target.

Corresponding issue:
#2945

Testing

Added test for when both source and target not set to make sure it targets body as expected

Checklist

• I have read the contribution guidelines
• I have targeted this PR against the correct branch (master for website changes, dev for
  source changes)
• This is either a bugfix, a documentation update, or a new feature that has been explicitly
  approved via an issue
• I ran the test suite locally (npm run test) and verified that it succeeded