The consumer on the camel-slack component is not checking for error responses coming from the Slack API. Under some circumstances this can be problematic and hide messages that would be helpful for the user to diagnose problems on his/her setup of the app/bot account.
One example that causes this problem is when the user creates a bot and does not give the bot the channels:read scope/permission. In this case the component throws a NullPointerException because it looks for an element on the json response that does not exist.
It seems it can also happen when trying to read the channel messages without the channels:history scope, although, in this case the component does not throw any exception.