 	open func updateTitleView() {
         guard let selectedGroupId = self.selectedGroupId else { return }
         
-        let group = self.imagePickerController.groupDataManager.fetchGroup(with: selectedGroupId)
+        guard let group = self.imagePickerController.groupDataManager.fetchGroup(with: selectedGroupId) else {
+            assertionFailure("Expect group")
+            return
+        }
 		self.title = group.groupName
 		
 		let groupsCount = self.imagePickerController.groupDataManager.groupIds?.count ?? 0

        let delta = abs(preheatRect.midY - self.previousPreheatRect.midY)
        guard delta > view.bounds.height / 3 else { return }
        
        let group = self.imagePickerController.groupDataManager.fetchGroup(with: selectedGroupId)
        
        // Compute the assets to start caching and to stop caching.
        let (addedRects, removedRects) = self.differencesBetweenRects(self.previousPreheatRect, preheatRect)

    public func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
		guard let selectedGroupId = self.selectedGroupId else { return 0 }
		
        guard let group = self.imagePickerController.groupDataManager.fetchGroup(with: selectedGroupId) else {
            assertionFailure("Expect group")
            return 0
        }
        return group.totalCount + (self.hidesCamera ? 0 : 1)
    }
    
