Merge pull request #20097 from akka/wip-19177-npe-persistent-fsm-patriknw

avoid NPE in recoveryRunning, #19177

akka-actor/src/main/scala/akka/actor/FSM.scala

@@ -515,17 +515,24 @@ trait FSM[S, D] extends Actor with Listeners with ActorLogging {
    *
    * @see [[#startWith]]
    */
-  final def initialize(): Unit = makeTransition(currentState)
+  final def initialize(): Unit =
+    if (currentState != null) makeTransition(currentState)
+    else throw new IllegalStateException("You must call `startWith` before calling `initialize`")
 
   /**
    * Return current state name (i.e. object of type S)
    */
-  final def stateName: S = currentState.stateName
+  final def stateName: S = {
+    if (currentState != null) currentState.stateName
+    else throw new IllegalStateException("You must call `startWith` before using `stateName`")
+  }
 
   /**
    * Return current state data (i.e. object of type D)
    */
-  final def stateData: D = currentState.stateData
+  final def stateData: D =
+    if (currentState != null) currentState.stateData
+    else throw new IllegalStateException("You must call `startWith` before using `stateData`")
 
   /**
    * Return next state data (available in onTransition handlers)

akka-persistence/src/main/scala/akka/persistence/Eventsourced.scala

@@ -427,7 +427,10 @@ private[persistence] trait Eventsourced extends Snapshotter with PersistenceStas
   /**
    * Returns `true` if this persistent actor is currently recovering.
    */
-  def recoveryRunning: Boolean = currentState.recoveryRunning
+  def recoveryRunning: Boolean = {
+    // currentState is null if this is called from constructor
+    if (currentState == null) true else currentState.recoveryRunning
+  }
 
   /**
    * Returns `true` if this persistent actor has successfully finished recovery.

akka-persistence/src/main/scala/akka/persistence/fsm/PersistentFSMBase.scala

@@ -309,17 +309,23 @@ trait PersistentFSMBase[S, D, E] extends Actor with Listeners with ActorLogging
    *
    * @see [[#startWith]]
    */
-  final def initialize(): Unit = makeTransition(currentState)
+  final def initialize(): Unit =
+    if (currentState != null) makeTransition(currentState)
+    else throw new IllegalStateException("You must call `startWith` before calling `initialize`")
 
   /**
    * Return current state name (i.e. object of type S)
    */
-  final def stateName: S = currentState.stateName
+  final def stateName: S =
+    if (currentState != null) currentState.stateName
+    else throw new IllegalStateException("You must call `startWith` before using `stateName`")
 
   /**
    * Return current state data (i.e. object of type D)
    */
-  final def stateData: D = currentState.stateData
+  final def stateData: D =
+    if (currentState != null) currentState.stateData
+    else throw new IllegalStateException("You must call `startWith` before using `stateData`")
 
   /**
    * Return all defined state names