Pass files from input-element to plupload (Add folder)

I want to upload all files of a folder. Since plupload does not offer this functionality, I have an input like this

<input type="file" name="files[]" id="files" multiple directory="" webkitdirectory="" mozdirectory="">

that stores all files out of a chosen folder. I now want to load these to my uploader

uploader = new plupload.Uploader({});

When I try to do so like

$('#files').change(function (){
    if ($(this).prop('files').length > 0)
    {
        uploader.addFile($('#files').prop('files')[0]);
    }
});

it results in

Uncaught TypeError: Cannot read property 'processing' of null

at

uploader.start();

How can I pass file references from my input-element to the plupload-Uploader?