无法从dropzone.js并行上传获取服务器响应

Question

I'm trying to get the server response from a set of uploads using dropzone.js parallel uploading so that I can maintain the uploader's intended file order as I register the files in a mySQL database. My files are being uploaded just fine, and the "successmultiple" event is being fired as expected - but server response is empty.

jQuery(document).ready(function() {
    Dropzone.autoDiscover = false;
    var filedrop = new Dropzone("#filedrop", {
        parallelUploads: 2,
        uploadMultiple: true,
        init: function() {
            this.on("successmultiple", function(files, response) {
                console.log(response);
            });
        },
        url: "upload2.php"
    });
});

If I assume the response is json and attempt to parse it as such:

               var json = $.parseJSON(response);
                $(json).each(function(i,val){
                        $.each(val,function(k,v){
                                console.log(k+" : "+ v);     
                        });
                });

I get a Uncaught SyntaxError: Unexpected end of JSON input error. Is the response empty because I haven't echo'd anything from my upload2.php file? I'd like to get a response that gives me information about file order while retaining the important ability to do parallel uploads. Am I completely barking up the wrong tree trying to determine the file order with server response? Are there any dropzone.js experts in the wings?