realm-swift: EXC_BAD_ACCESS crash when using NSOutlineView

I’m creating an NSOutlineView populated by objects saved on Realm. The object is called Person. And this is how it looks:

@interface Person : RLMObject

@property NSString *name;
@property NSInteger indent;
@property NSInteger order;

// Ignored properties
@property NSArray *contacts;

The contacts array returns a query. Those contacts are child of the person, but they also have the same object class, Person.

And this is the view controller:

#import "MainWindowController.h"
#import "Person.h"

@interface MainWindowController () <NSOutlineViewDataSource, NSOutlineViewDelegate>

@property (strong) IBOutlet NSOutlineView *outlineView;

@property (nonatomic, strong) RLMResults *array;
@property (nonatomic, strong) RLMNotificationToken *notification;

@end

@implementation MainWindowController

- (id)init
{
    self = [super initWithWindowNibName:@"MainWindow"];

    if (self) {
        __weak typeof(self) weakSelf = self;

        self.notification = [RLMRealm.defaultRealm addNotificationBlock:^(NSString *note, RLMRealm *realm) {
            [weakSelf.outlineView reloadData];
        }];

        self.array = [[Person objectsWhere:@"indent == 1"] sortedResultsUsingProperty:@"order" ascending:YES];
    }

    return self;
}

- (void)windowDidLoad
{
    [super windowDidLoad];

    [self.outlineView setRowHeight:50];
}

#pragma mark - NSOutlineView

- (id)outlineView:(NSOutlineView *)outlineView child:(NSInteger)index ofItem:(id)item
{
    if (item == nil) {
        return self.array[index];
    }
    else if ([item isKindOfClass:[Person class]]) {
        return [item contacts][index];
    }

    return nil;
}

- (BOOL)outlineView:(NSOutlineView *)outlineView isItemExpandable:(id)item
{
    if (item == nil) {
        return NO;
    }
    else if ([item isKindOfClass:[Person class]]) {
        return [item contacts].count > 0;
    }

    return NO;
}

- (NSInteger)outlineView:(NSOutlineView *)outlineView numberOfChildrenOfItem:(id)item
{
    if (item == nil) {
        return self.array.count;
    }
    else if ([item isKindOfClass:[Person class]]) {
        return [item contacts].count;
    }

    return 0;
}

- (NSView *)outlineView:(NSOutlineView *)outlineView viewForTableColumn:(NSTableColumn *)tableColumn item:(id)item
{
    NSView *cellView = [[NSView alloc] initWithFrame:NSMakeRect(0, 0, 250, 0)];

    NSTextField *titleTextField = [[NSTextField alloc] initWithFrame:NSMakeRect(0, 15, 250, 18)];
    [titleTextField setEditable:NO];
    [titleTextField setBordered:NO];
    titleTextField.backgroundColor = [NSColor clearColor];
    titleTextField.textColor = [NSColor blackColor];
    titleTextField.focusRingType = NSFocusRingTypeNone;
    titleTextField.stringValue = [item name];
    [cellView addSubview:titleTextField];

    return cellView;
}

The “root” cells are displayed correctly, but then, when I click the arrow to expand one of those root cells, the app crashes with an EXC_BAD_ACCESS error. I used NSZombie to know more about this crash, and that’s what it tells me:

-[RLMAccessor_v0_Person retain]: message sent to deallocated instance 0x60800016ba00

I debugged all the data source methods of the NSOutlineView when tapping the arrow to expand the row, but no method is called.

Any idea of what’s happening?