Call to a member function move() on null

I suspect that the solution may be obvious but I Am not winning. Please assist to solve this issue. I want to save a book with image(image works well) and pdf (which is not uploading because of the error)

How can save/store pdf and image at the same time?

 public function store(Request $request)
    {
        $this->validate($request, [
            'name' => 'required',
            'description' => 'required',
            'price' => 'required',
            'image' => 'required|image',
            'file_name' => 'required',
        ]);
        $book = new Book;
        // Upload Image
        if($request->hasFile('image')){
            $image_tmp = Input::file('image');
            if ($image_tmp->isValid()) {
                // Upload Images after Resize
                $extension = $image_tmp->getClientOriginalExtension();
                $book_image_new_name = rand(111,99999).'.'.$extension;
                $image = 'uploads/books'.'/'.$book_image_new_name;
                Image::make($image_tmp)->save($image);
                $book->image = $book_image_new_name;
            }
        }
        //Upload i want to upload a pdf please help
        $file = $request->file('pdf');
        $destinationPath = 'uploads/books';
        $file->move($destinationPath,$file->getClientOriginalName()); // this line here is the problem or throws an error

        $book->name = $request->name;
        $book->description = $request->description;
        $book->price = $request->price;
        $book->pages = $request->pages;
        $book->author = $request->author;
        $book->isbn = $request->isbn;
        $book->publisher = $request->publisher;
        $book = $request->file('pdf');
        $book->image = 'uploads/books/' . $book_image_new_name;
        $book->save();
        Session::flash('success', 'Book created.');

        return redirect()->back()->with('msg','Book added successfully');

    }