Loading an image from the database with play! scala

gistfile1.scala

/**
* Loads the specified documentInstance, the current authenticated user is retrieved
* to check that it's the document owner.
* Play! Framework with latest Scala module.
* Nicolas Martignole - 09/08/2011
*/    
def loadImage(di:Option[Long]) = {
        import play.utils.Scala.MayErr._

        val result=(
            for (
                docInstanceId:Long <- di.toRight(Error("Parameter not found"));
                val maybeUser = session("connected").flatMap(Webuser.lookup(_));
                webuser<-maybeUser.toRight(Unauthorized) ;
                val maybeDocInstance = DocumentInstance.find("id={id} and owner={owner}").on("id"->docInstanceId,"owner"->webuser.id()).first() ;
                docInstance <- maybeDocInstance.toRight(NotFound("document instance not found"));

                val zeFile:VirtualFile = VirtualFile.fromRelativePath(docInstance.url);
                val _ = {
                    // why do I need a val _ ?
                   Http.Response.current().setContentTypeIfNotSet("image/jpeg");
                }
            ) yield zeFile)

        result.fold(identity, f=>f.inputstream())
    }

@glaforge are you sure you know what it is doing?