new.m

    [[[[RACAble(self.eventManagedObjectID) distinctUntilChanged] map:^TBDMilestone *(NSManagedObjectID *nextEventManagedObjectID) {
        @strongify(self);

        if (TCBIsEmpty(nextEventManagedObjectID)) {
            return nil;
        }

        NSError *objectRetrievalError;
        TBDMilestone *milestone = (TBDMilestone *)[self.controllerManagedObjectContext existingObjectWithID:nextEventManagedObjectID error:&objectRetrievalError];

        if (TCBIsEmpty(milestone)) {
            TCBLogError(objectRetrievalError);
        }

        return milestone;
    }] deliverOn:[RACScheduler mainThreadScheduler]] subscribeNext:^(TBDMilestone *milestone) {
        @strongify(self);
        self.label = milestone.label;
        self.photo = [UIImage imageWithData:milestone.photo.data];
        self.startDate = TCBIsNotEmpty(milestone) ? milestone.startedAt :[NSDate date];
    }];

old.m

    RAC(self.milestone) = [[RACAble(self.eventManagedObjectID) distinctUntilChanged] map:^TBDMilestone *(NSManagedObjectID *nextEventManagedObjectID) {
        @strongify(self);

        if (TCBIsEmpty(nextEventManagedObjectID)) {
            return nil;
        }

        NSError *objectRetrievalError;
        TBDMilestone *milestone = (TBDMilestone *)[self.controllerManagedObjectContext existingObjectWithID:nextEventManagedObjectID error:&objectRetrievalError];

        if (TCBIsEmpty(milestone)) {
            TCBLogError(objectRetrievalError);
        }

        return milestone;
    }];
    
    [RACAbleWithStart(self.milestone) subscribeNext :^(TBDMilestone *nextMilestone) {
        @strongify(self);
        self.label = nextMilestone.label;
        self.photo = [UIImage imageWithData:nextMilestone.photo.data];
        self.startDate = TCBIsNotEmpty(nextMilestone) ? nextMilestone.startedAt :[NSDate date];
    }];