IPhone : Undefined selector with Objective-C runtime - blocks

I'm trying to create a function where multiple times I do the same thing. I've deceided to go with a block this time. However after writing following code:

- (BOOL)readyForProcessing {
    void (^notDeclaredError)(id) = ^(id missingObject) {
        NSString *missingObjectName = NSStringFromSelector(@selector(missingObject));
        NSString *errorDescription = [NSString stringWithFormat:@"You need to provide %@ property", missingObjectName];
        [self configureErrorWithLocalizedDescription:errorDescription];
    };

    if (!self.delegate) notDeclaredError(self.delegate);

    return self.error ? NO : YES;
}

I get a warning in the line, where I declare missingObjectName.

 Undeclared selector 'missingObject'

I know it will probably try to make a NSString from missingObject instead of delegate. How to pass it this way, that the output will be delegate and the code will be inside the block?