Replying to [comment:1 dmethvin]:
Why are you saying
dataType: 'json' if the returned data type isn't JSON? If you expect text, say it's text.
First, thank you for replying. I appreciate your time considering this.
We are sometimes asked to interact with servers not under our control. One such server returns json mime-type when it has new data and text mime-type when it wishes to return "". The correctness of this is worthy of debate. But it is immutable for the purposes of discussing this jQuery issue.
If I ask for dataType: text, then I lose the benefits of automatic JSON parsing. If I ask for dataType: json, then I get errors when parsing "".
I see an undocumented difference in behavior between 1.8 and 1.9+. I mention it because it's what good citizens do. I leave it to others to decide: a) to put this compatibility behavior back into 1.9+, b) to add detection of the change to jquery-migrate, c) add the changed behavior to release notes, or d) do nothing.