Slack import no longer works in 4.x

Description:

Slack import no longer works on any 4.x version

Steps to reproduce:

1. Obtain a slack export
2. Use import from file or public server url
3. Start import
4. After file is loaded and you select the messages/channels/users

Expected behavior:

Import to work

Actual behavior:

Import fails

Server Setup Information:

• Version of Rocket.Chat Server: 4.4.1
• Operating System: Ubuntu 18.04
• Deployment Method: docker
• Number of Running Instances: 1
• DB Replicaset Oplog: 1
• NodeJS Version: 14
• MongoDB Version: 4.2

Client Setup Information

• Desktop App or Browser Version: Firefox 97
• Operating System: Windows

Additional context

File is loaded correctly but starting the import fails with error. Even the older backup files that were previously successfully imported with 3.x no longer work on 4.x. Manually inspecting slack export json files don't show up anything related to "" objects.

Relevant logs:

rocketchat_1 | {"level":50,"time":"2022-02-06T17:23:39.954Z","pid":1436,"hostname":"735a54cf786a","name":"","name":"Slack Importer","err":{"type":"Error","message":"object [\"\"] is not a valid ObjectId","stack":"Error: object [\"\"] is not a valid ObjectId\n at serializeObjectId (/app/bundle/programs/server/npm/node_modules/meteor/npm-mongo/node_modules/bson/lib/bson/parser/serializer.js:287:11)\n at serializeInto (/app/bundle/programs/server/npm/node_modules/meteor/npm-mongo/node_modules/bson/lib/bson/parser/serializer.js:941:17)\n at serializeObject (/app/bundle/programs/server/npm/node_modules/meteor/npm-mongo/node_modules/bson/lib/bson/parser/serializer.js:347:18)\n at serializeInto (/app/bundle/programs/server/npm/node_modules/meteor/npm-mongo/node_modules/bson/lib/bson/parser/serializer.js:947:17)\n at serializeObject (/app/bundle/programs/server/npm/node_modules/meteor/npm-mongo/node_modules/bson/lib/bson/parser/serializer.js:347:18)\n at serializeInto (/app/bundle/programs/server/npm/node_modules/meteor/npm-mongo/node_modules/bson/lib/bson/parser/serializer.js:729:17)\n at serializeObject (/app/bundle/programs/server/npm/node_modules/meteor/npm-mongo/node_modules/bson/lib/bson/parser/serializer.js:347:18)\n at serializeInto (/app/bundle/programs/server/npm/node_modules/meteor/npm-mongo/node_modules/bson/lib/bson/parser/serializer.js:947:17)\n at BSON.serialize (/app/bundle/programs/server/npm/node_modules/meteor/npm-mongo/node_modules/bson/lib/bson/bson.js:64:28)\n at Msg.serializeBson (/app/bundle/programs/server/npm/node_modules/meteor/npm-mongo/node_modules/mongodb/lib/core/connection/msg.js:127:22)\n at Msg.makeDocumentSegment (/app/bundle/programs/server/npm/node_modules/meteor/npm-mongo/node_modules/mongodb/lib/core/connection/msg.js:119:33)\n at Msg.toBin (/app/bundle/programs/server/npm/node_modules/meteor/npm-mongo/node_modules/mongodb/lib/core/connection/msg.js:105:25)\n at MessageStream.writeCommand (/app/bundle/programs/server/npm/node_modules/meteor/npm-mongo/node_modules/mongodb/lib/cmap/message_stream.js:55:28)\n at Connection.write (/app/bundle/programs/server/npm/node_modules/meteor/npm-mongo/node_modules/mongodb/lib/cmap/connection.js:373:26)\n at _command (/app/bundle/programs/server/npm/node_modules/meteor/npm-mongo/node_modules/mongodb/lib/core/wireprotocol/command.js:125:10)\n at command (/app/bundle/programs/server/npm/node_modules/meteor/npm-mongo/node_modules/mongodb/lib/core/wireprotocol/command.js:28:5)\n at writeCommand (/app/bundle/programs/server/npm/node_modules/meteor/npm-mongo/node_modules/mongodb/lib/core/wireprotocol/write_command.js:56:3)\n at Object.update (/app/bundle/programs/server/npm/node_modules/meteor/npm-mongo/node_modules/mongodb/lib/core/wireprotocol/index.js:9:5)\n at Connection.update (/app/bundle/programs/server/npm/node_modules/meteor/npm-mongo/node_modules/mongodb/lib/cmap/connection.js:195:8)\n at /app/bundle/programs/server/npm/node_modules/meteor/npm-mongo/node_modules/mongodb/lib/core/sdam/server.js:490:13\n at Object.callback (/app/bundle/programs/server/npm/node_modules/meteor/npm-mongo/node_modules/mongodb/lib/cmap/connection_pool.js:345:7)\n at processWaitQueue (/app/bundle/programs/server/npm/node_modules/meteor/npm-mongo/node_modules/mongodb/lib/cmap/connection_pool.js:468:23)"},"msg":"object [\"\"] is not a valid ObjectId"}

Start by reproducing the Slack import through the file or public server URL, then inspect the Slack Importer path associated with the logged invalid ObjectId error. Compare the 4.x behavior with the previously working 3.x backup files; done means selecting messages, channels, and users completes the import without the BSON serialization failure.