In JsonResponse::setData json_encode is called then and then JsonEncode::update is called to deal with setting up the content.

If no JS callback is specified and json_encode fails -- returns false -- Response::setContent throws an UnexpectedValueException saying that only strings or objects that have a __toString method are allowed.

I ran into this with an invalid UTF8 character that came out of MySQL.

Seems like this could be improved by checking for a false result on the json_encode call and using json_last_error to generate a nicer error message.

Would that be too detailed for JsonResponse? Should it be up to the caller to make sure they give JsonResponse::setData something valid? Even if it's very hard to tell that something may not work?