SwiftValue: ctFontRef unrecognized selector sent to instance

I am doing an chatting app by using Quick blox. I am not an expecting in code. when i run the app. The app gets crashed. I got an error. Chatting Message[1806:27316] -[_SwiftValue ctFontRef]: unrecognized selector sent to instance 0x600000253020 2017-05-16 10:23:38.982 Chatting Message[1806:27316] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[_SwiftValue ctFontRef]: unrecognized selector sent to instance 0x600000253020'

override func collectionView(_ collectionView: QMChatCollectionView, dynamicSizeAt indexPath: IndexPath, maxWidth: CGFloat) -> CGSize
    {
        let item: QBChatMessage? = chatDataSource.message(for: indexPath)
        let viewClass: AnyClass = self.viewClass(forItem: item!)
        var size: CGSize?
        if viewClass == QMChatAttachmentIncomingCell.self || viewClass == QMChatAttachmentOutgoingCell.self
        {
            size = CGSize(width: CGFloat(min(200, maxWidth)), height: CGFloat(200))
        }
        else
        {
//            let attributedString: NSAttributedString? = self.attributedString(forItem: item!)
//            size = TTTAttributedLabel.sizeThatFitsAttributedString(attributedString, withConstraints: CGSize(width: maxWidth, height: CGFloat(MAXFLOAT)), limitedToNumberOfLines: 0)
        }
        size = CGSize(width: CGFloat(min(200, maxWidth)), height: CGFloat(200))
        return size!
    }

    override func collectionView(_ collectionView: QMChatCollectionView, minWidthAt indexPath: IndexPath) -> CGFloat
    {
        let item: QBChatMessage? = chatDataSource.message(for: indexPath)
        var size: CGSize?
        size = CGSize(width: CGFloat(1000), height: CGFloat(10000))
        if item != nil
        {
         let attributedString: NSAttributedString? = item?.senderID == senderID ? bottomLabelAttributedString(forItem: item!) : topLabelAttributedString(forItem: item!)
   size = TTTAttributedLabel.sizeThatFitsAttributedString(attributedString, withConstraints: CGSize(width: CGFloat(1000), height: CGFloat(10000)), limitedToNumberOfLines: 1)
        }
        return size!.width
    }

    override func collectionView(_ collectionView: QMChatCollectionView, layoutModelAt indexPath: IndexPath) -> QMChatCellLayoutModel
    {
        var layoutModel: QMChatCellLayoutModel = super.collectionView(collectionView, layoutModelAt: indexPath)
        let item: QBChatMessage? = chatDataSource.message(for: indexPath)
        layoutModel.avatarSize = CGSize(width: CGFloat(0.0), height: CGFloat(0.0))
        if item != nil
        {
      let topLabelString: NSAttributedString? = topLabelAttributedString(forItem: item!)
   let size1 = TTTAttributedLabel.sizeThatFitsAttributedString(topLabelString, withConstraints: CGSize(width: collectionView.frame.width, height: CGFloat.greatestFiniteMagnitude), limitedToNumberOfLines: 1)
   layoutModel.topLabelHeight = size.height
        }
        return layoutModel
    }