- (MyObj * _Nonnull)initWithManagedObject:(NSManagedObject * _Nonnull)managedObject dataManager:(id<DataManagerProtocol> _Nonnull)dataManager;

@property (nonatomic, weak, readonly) id<DataManagerProtocol> dataManager;

- (MyObj *)initWithManagedObject:(NSManagedObject *)object dataManager:(id<RHDataManagerProtocol>)dataManager
{
    // TEST
    self = [super init];
    if (self) {
        // Both the following lines cause the warning.
        // Changing nullability has no effect.
        self.dataManager = dataManager;
        //_dataManager = dataManager;
    }
    return self;
}

@interface MyObj ()

@property (nonatomic, weak) id<DataManagerProtcol> dataManager;

@end

~.delegate = (id)self;