@dmethvin Actually, reading http://api.jquery.com/jQuery.parseJSON/ suggests to me that we can remove both the code and the test supporting `jQuery.parseJSON( null )`:
> Takes a well-formed JSON string and returns the resulting JavaScript object... Prior to jQuery 1.9, `$.parseJSON` returned `null` instead of throwing an error if it was passed an empty string, `null`, or `undefined`, even though those are not valid JSON.

It will, of course, continue to work on almost all native implementations (and everywhere as `jQuery.parseJSON( null + "" )`). jquery-migrate now patches it up as well, so I think core is all set.