mutating method sent to immutable object with userInfo (null) - ios5

Question

I want to clear all the data by fetch all records and delete them one by one:
- (void) clear{
for (Program *program in [self getAllProgram]){
[managedObjectContext deleteObject:program];
}
if (![managedObjectContext save:&error])
{
NSLog(#"Problem deleting program: %#", [error localizedDescription]);
}
}
- (NSArray *)getAllProgram{
NSFetchRequest *request = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Program"inManagedObjectContext:managedObjectContext];
[request setEntity:entity];
NSPredicate *predicate = [NSPredicate predicateWithFormat: #"freq = %#", self.freq];
[request setPredicate:predicate];
// Order the events by creation date, most recent first.
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:#"sid" ascending:YES];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
[request setSortDescriptors:sortDescriptors];
[sortDescriptor release];
[sortDescriptors release];
NSError *error = nil;
return [[managedObjectContext executeFetchRequest:request error:&error] mutableCopy];
}
The error is
CoreData: error: Serious application error. Exception was caught
during Core Data change processing. This is usually a bug within an
observer of NSManagedObjectContextObjectsDidChangeNotification.
-[__NSCFSet removeAllObjects]: mutating method sent to immutable object with userInfo (null)
Who can tell me the reason or tell me the one good practice ? thanks!

Answer 1

I suppose you have a fetched results controller somewhere. Set that controller's delegate to nil during the delete. I usually actually set the whole FRC to nil and update my whole data display after a large data change.
If that is not feasible, handle this case in the notification handler, like
if (!userInfo) return;