         return true
     }
 
-    private func react(cell: IssueCommentReactionCell, content: ReactionContent, isAdd: Bool) {
+    private func react(cell: IssueCommentReactionCell?, content: ReactionContent, isAdd: Bool) {
         guard let object = self.object else { return }
 
         let previousReaction = reactionMutation

    // MARK: DoubleTappableCellDelegate
    
    func didDoubleTap(cell: DoubleTappableCell) {
        guard let reactionCell = collectionContext?.cellForItem(at: numberOfItems() - 1, sectionController: self) as? IssueCommentReactionCell else {
            return
        }
        
        let reaction = ReactionContent.thumbsUp
        guard let reactions = reactionMutation ?? self.object?.reactions,
            !reactions.viewerDidReact(reaction: reaction)
            else { return }
        
        react(cell: reactionCell, content: reaction, isAdd: true)
    }

    // MARK: IssueCommentDetailCellDelegate

            add: isAdd
        )
        reactionMutation = result.viewModel

        cell?.perform(operation: result.operation, content: content)

        update(animated: true)
        generator.impactOccurred()
        client.react(subjectID: object.id, content: content, isAdd: isAdd) { [weak self] result in
