Even with a positive naming convention, you will have conditionals for the negative case, e.g. if (![str isEqualToString:@"myvalue"]) and falling into its block

Even with a positive naming convention, you will have conditionals for the negative case, e.g. if (![str isEqualToString:@"myvalue"]) and falling into its block is not desirable when str is nil. Personally I have had plenty of bugs around things being unexpectedly nil, but I can't think of a case like this where I executed a block unexpectedly.