If someone doesn't place 10 pieces of chametz for bedikah as the custom is to do, and says the bracha "al biur chametz" and then does bedikat chametz, but for some reason (maybe he cleaned his house really well before Pesach, or other cases), he does not find any chametz, would the bracha he made be a bracha levatala? This question is on Rishonim including the Rosh (look here) who explain that the main bracha of al biur chametz done before bedikah is actually on the bedika and we only say "al biur chametz" because its the start of the process.
Please explain why it is or isn't and bring sources, thanks.