Error Empty file upload result - problem with jQuery bulk file upload

I have problems with multiple file upload. I tried Paperclip with jQuery file uplad plugin and get the error mentioned in the title. Files get uploaded without problems, but I keep getting this embarrassing error.

Can somebody offer a solution to my problem or suggest alternative solution that can be implemented in 2 hours? My client is getting a bit uneasy now.

I have tried everything I could think of and in the end I have modified the model following this advice:
https://github.com/blueimp/jQuery-File-Upload/issues/365#issuecomment-13859210

My code can be found at:
https://github.com/bigos/chrisb-images/blob/master/app/models/upload.rb

relevant bit in my model looks like this:

def to_jq_upload

{

:files => [

{

:name => upload_file_name,

:type => upload_content_type,

:size => upload_file_size,

:url => upload.url,

:delete_url => upload_path(self),

:delete_type => "DELETE"

}

]

}

end

Fixed!!!
controller:
https://github.com/bigos/chrisb-images/blob/master/app/controllers/photos_controller.rb

def create

@photo = Photo.new(params[:photo])

respond_to do |format|

if @photo.save

format.html { render :json => [@photo.to_jq_upload].to_json,

:content_type => 'text/html',

:layout => false

}

format.json { render json: {files: [@photo.to_jq_upload] }}

else

format.html { render action: "new" }

format.json { render json: @photo.errors, status: :unprocessable_entity }

end

end

end

model:
https://github.com/bigos/chrisb-images/blob/master/app/models/photo.rb