Object #<Object> has no method 'split'

thanks for the awesome package, i have following error after i upload an image. Image was save under tmpDir but not uploadDir. Any clue where causing the error?

template.html

{{>upload_bootstrap fileTypes='image/*' formData=myFormData}}

template.js helper

myFormData: function() {
    return { directoryName: 'images', prefix: this._id, _id: this._id }
}

server/init.js

Meteor.startup(function () {
    UploadServer.init({
        tmpDir: '/www/public/tmp',
        uploadDir: '/www/public/',
        checkCreateDirectories: true,
        getDirectory: function(fileInfo, formData) {
            console.log('\n\ngetDirectory:');
            console.log(fileInfo);
            console.log(formData);
            return formData;
        },
        getFileName: function(fileInfo, formData) {
            console.log('\n\getFileName:');
            console.log(fileInfo);
            console.log(formData);
            return fileInfo;
        },
        finished: function(fileInfo, formData) {
            console.log('\n\nfinished:');
            console.log(fileInfo);
            console.log(formFields);
        },
        cacheTime: 100
    })
});

I20150923-10:05:10.863(8)? 
I20150923-10:05:10.863(8)? 
I20150923-10:05:10.863(8)? getDirectory:
I20150923-10:05:10.863(8)? poster.jpg
I20150923-10:05:10.863(8)? { directoryName: 'images',
I20150923-10:05:10.863(8)?   prefix: '8HFTt4j4SEcfGjiLJ',
I20150923-10:05:10.863(8)?   _id: '8HFTt4j4SEcfGjiLJ' }
W20150923-10:05:11.158(8)? (STDERR) TypeError: Object #<Object> has no method 'split'
W20150923-10:05:11.158(8)? (STDERR)     at IncomingForm.<anonymous> (packages/tomi:upload-server/upload_server.js:248:1)
W20150923-10:05:11.158(8)? (STDERR)     at IncomingForm.emit (events.js:98:17)
W20150923-10:05:11.158(8)? (STDERR)     at /Users/keep/.meteor/packages/tomi_upload-server/.1.0.3.1b7hz87++os+web.browser+web.cordova/npm/node_modules/formidable/lib/incoming_form.js:228:12
W20150923-10:05:11.158(8)? (STDERR)     at WriteStream.<anonymous> (/Users/keep/.meteor/packages/tomi_upload-server/.1.0.3.1b7hz87++os+web.browser+web.cordova/npm/node_modules/formidable/lib/file.js:70:5)
W20150923-10:05:11.158(8)? (STDERR)     at WriteStream.g (events.js:180:16)
W20150923-10:05:11.158(8)? (STDERR)     at WriteStream.emit (events.js:117:20)
W20150923-10:05:11.158(8)? (STDERR)     at finishMaybe (_stream_writable.js:360:12)
W20150923-10:05:11.159(8)? (STDERR)     at afterWrite (_stream_writable.js:280:5)
W20150923-10:05:11.159(8)? (STDERR)     at onwrite (_stream_writable.js:270:7)
W20150923-10:05:11.159(8)? (STDERR)     at WritableState.onwrite (_stream_writable.js:97:5)

tomitrescak / meteor-uploads

Object #<Object> has no method 'split' #153