Fixed BUG-18 -> cannot find book

main.py

@@ -439,13 +439,13 @@ def new_book():
             book = Book( title=request.form['title'], owned=request.form['owned'], covertype=request.form['covertype'], condition=request.form['condition'], publisher=request.form['publisher'], year_published=request.form['year_published'], rating=request.form['rating'], notes=request.form['notes'], blurb=request.form['blurb'], genre=book_genres, author=book_authors )
             db.session.add(book)
             db.session.commit()
-			# this is a sub-book we have added
+            # this is a sub-book we have added
             if 'parent_id' in request.form:
                 db.engine.execute( "insert into book_sub_book_link ( book_id, sub_book_id, sub_book_num ) values ( {}, {}, (select COALESCE(MAX(sub_book_num),0)+1 from book_sub_book_link where book_id = {}) )".format( request.form['parent_id'], book.id, request.form['parent_id'] ) )
                 parent=Book.query.get(request.form['parent_id'])
                 if len(parent.series) > 0:
                     # we have added a sub-book to something in a series
-					# already, so add a bsl for the next book_num
+                    # already, so add a bsl for the next book_num
                     for s in parent.bsl:
                         db.engine.execute( "insert into book_series_link ( series_id, book_id, book_num ) values ( {}, {}, (select COALESCE(MAX(book_num),0)+1 from book_series_link where series_id={}) )".format( s.series_id, book.id, s.series_id ) )
                 db.session.commit()
@@ -593,6 +593,11 @@ def book(id):
             st.SetMessage(message)
     else:
         book = Book.query.get(id)
+        if book == None:
+            st.SetAlert("danger")
+            st.SetMessage("Cannot find Book (id={})".format(id))
+            return render_template("base.html", alert=st.GetAlert(), message=st.GetMessage())
+
         book_form=BookForm(obj=book)
 
     author_list = GetAuthors()