Q. One who is doing bedikas chametz and knows that he will not find a crumb of chametz (and he doesn’t have anything to hide), should he refrain from blessing?
A. Rema (432: 2) writes that the minhag is to place some pieces of chometz before the search so the brocho will not be in vain in case he does not find any chometz. But then he adds that even in case he did not place any, the brocho is not considered lebatala, since that is the nature of this mitzva; to search and find if there is chometz and if there isn’t the purpose was already reached. Mishna Berura (ibid. 13) further explains, in the name of the Taz, that the brocho then, will also rest on the future burning of the chometz to be done next day, and adds that this is the accepted opinion of the Acharonim.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a