I have configure sftp for drop folder but getting this error any one please if tell me whats the problem
==> /opt/kaltura/log/kaltura_apache_errors.log <==
[Thu Aug 02 18:12:21.222003 2018] [:error] [pid 29028] [client 173.249.21.27:56838] PHP Fatal error: Uncaught Error: Call to a member function lock() on null in /opt/kaltura/app/plugins/drop_folder/lib/kDropFolderAllocator.php:105\nStack trace:\n#0 /opt/kaltura/app/plugins/drop_folder/lib/kDropFolderAllocator.php(128): kDropFolderAllocator::lockDropFolder(8, 30000)\n#1 /opt/kaltura/app/plugins/drop_folder/lib/kDropFolderAllocator.php(73): kDropFolderAllocator::allocateDropFolderFromList(Object(kMemcacheCacheWrapper), Array, ‘drop_folder_lis…’, 30000)\n#2 /opt/kaltura/app/plugins/drop_folder/services/DropFolderService.php(243): kDropFolderAllocator::getDropFolder(’’, 30000)\n#3 /opt/kaltura/app/api_v3/lib/reflection/KalturaActionReflector.php(233): DropFolderService->getExclusiveDropFolderAction(’’, 30000)\n#4 /opt/kaltura/app/api_v3/lib/KalturaDispatcher.php(130): KalturaActionReflector->invoke(Array)\n#5 /opt/kaltura/app/api_v3/lib/KalturaFrontController.php(113): KalturaDispatcher->dispatch(‘dropfolder_drop…’, ‘getexclusivedro…’, Array)\n#6 /opt/kaltura/app/api_v3/web/index.php(31): KalturaFrontController- in /opt/kaltura/app/plugins/drop_folder/lib/kDropFolderAllocator.php on line 105