The method handling file upload, get null pointer for the File param

   I am using scala, the play framework version is: play! 1.1-unstable-r1011
   In the file upload method the File is alway Null.
   Following is the code I using to handle the uploaded file.

            def uploadSlides(slides: File,title: String){
               println("Meeting ID:"+mid+",title:"+title+",File:"+slides);
            }