isEqualToString returning NO in iOS7 and working fine on iOS 5& 6

isEqualToString returning NO in iOS7 and working fine on iOS 5& 6

I am using following code: This code working fine till iOS 6 but on iOS 7
it is always returning NO. I changed isEqualToString with isEqual, but
still I am getting same result. On iOS 7 my code not working.
NSInteger documentIndex = [documentDict indexOfObjectPassingTest:^BOOL(id
obj, NSUInteger idx, BOOL *stop) {
NSDictionary* document = (NSDictionary*)obj;
NSString* docName = [document objectForKey:@"key"];
if([docName isEqualToString:@"MyItem"]){
return YES;
}else{
return NO;
}
}];
Can anyone tell me the reason why it is not working on iOS 7