TypeError: Argument 2 of FormData.append is not an object.
formData.append(this._getParamName(i), files[i], "");

<script>
 Dropzone.options.myDropzone = {
      autoProcessQueue: false,
      uploadMultiple: true,
      parallelUploads: 100,
      maxFiles: 1,
      maxFilesize: 10, //mb
      acceptedFiles: 'image/*',
      addRemoveLinks: true,
      autoDiscover: false,
      previewsContainer: '.dropzone-previews',
      clickable: '.dz-clickable',  to showup the file select dialog box

      accept: function(file, done) {
                done();
            },

      // The setting up of the dropzone
      init: function() {
            var myDropzone = this;

            this.on("error", function(file, message) {
                alert(message);
                this.removeFile(file);
            });

      // Get Files from Server
      $.getJSON('listfiles', {aid: ID}, function(data) {

                if(data[0] != false)
                {
                      $.each(data, function(key, val) {

                        var mockFile = { name: val.name, size: 11 };
                        myDropzone.options.addedfile.call(myDropzone, mockFile);
                        myDropzone.options.thumbnail.call(myDropzone, mockFile, "/uploads/tmp/" + val.name);
                        myDropzone.files.push(mockFile);

                      });

                      var existingFileCount = myDropzone.files.length; // The number of files already uploaded
                      myDropzone.options.maxFiles = myDropzone.options.maxFiles - existingFileCount;

                }
            });

      $('#myDropzone').on("submit", function(e) {
                e.preventDefault();
                e.stopPropagation();

                if (myDropzone.getQueuedFiles().length > 0) {
                     myDropzone.processQueue();
                } else {
                     myDropzone.uploadFiles([]); //send empty
                }
      });

     this.on("removedfile", function(file) {

              $.ajax({
                    url: 'deleteimage',
                    cache: true,
                    dataType: 'json',
                    data:  { aid: advertID,iid: file.name  },
              });
                    var existingFileCount = myDropzone.files.length; // The number of files already uploaded
                    myDropzone.options.maxFiles = myDropzone.options.maxFiles + 1;

            });

if (files[0].status === Dropzone.CANCELED) {

if (files[0] && files[0].status === Dropzone.CANCELED) {

formData.append(this._getParamName(i), files[i], files[i].name);

if(typeof files[i] != "undefined"){
       formData.append(this._getParamName(i), files[i], files[i].name);
  }else{
       formData.append(this._getParamName(i), files[i], "");
  }