How to debug a NullPointerException in a Scala Akka Actor when accessing a mutable Map?
I'm stuck trying to I've been struggling with this for a few days now and could really use some help... I've hit a wall trying to After trying multiple solutions online, I still can't figure this out. I've looked through the documentation and I'm still confused about I'm working with a `NullPointerException` in my Scala Akka Actor when I try to access a mutable `Map` that is supposed to hold some state... My actor is designed to manage a collection of user sessions, each identified by a unique session ID. I've declared the map as a `var` at the class level, but it seems to be `null` at runtime when I attempt to access it. Here's the relevant part of my code: ```scala import akka.actor.Actor class SessionManager extends Actor { private var sessions: Map[String, String] = _ override def preStart(): Unit = { sessions = Map.empty // Initialize the sessions map } def receive: Receive = { case "getSession" => val sessionId = "someSessionId" val sessionData = sessions.get(sessionId) sender() ! sessionData.getOrElse("Session not found") } } ``` I've confirmed that the `preStart` method runs, and I can see `sessions` being initialized, yet when I send the `"getSession"` message, I'm still getting a `NullPointerException`. I also tried to log the contents of the `sessions` map right before I access it, and it shows as `null`. I suspect this might be due to the way the actor's lifecycle works or perhaps an scenario with concurrency because the method accessing the map is running in parallel with other messages. I've tried making the `sessions` map a `ConcurrentHashMap`, but the behavior continues. Is there a best practice for managing mutable state in Akka actors that could prevent this scenario? Any insights or suggestions on how to resolve this would be greatly appreciated. I am using Scala 2.13.6 and Akka 2.6.16. For context: I'm using Scala on Ubuntu. How would you solve this? My development environment is macOS. Any feedback is welcome! I'm working in a Windows 10 environment. Is there a simpler solution I'm overlooking?