Removing the naught default in code of the failure detector and changed so that the AccrualFailureDetectors constructor matches what the instantiator expects

akka-cluster/src/main/resources/reference.conf

@@ -59,7 +59,7 @@ akka {
       # network drop.
       acceptable-heartbeat-pause = 3s
 
-      implementation-class = ""
+      implementation-class = "akka.cluster.AccrualFailureDetector"
 
       max-sample-size = 1000
     }

akka-cluster/src/main/scala/akka/cluster/Cluster.scala

@@ -403,14 +403,12 @@ object Cluster extends ExtensionId[Cluster] with ExtensionIdProvider {
   override def createExtension(system: ExtendedActorSystem): Cluster = {
     val clusterSettings = new ClusterSettings(system.settings.config, system.name)
 
-    val failureDetector = clusterSettings.FailureDetectorImplementationClass match {
-      case None ⇒ new AccrualFailureDetector(system, clusterSettings)
-      case Some(fqcn) ⇒
-        system.dynamicAccess.createInstanceFor[FailureDetector](
-          fqcn, Seq((classOf[ActorSystem], system), (classOf[ClusterSettings], clusterSettings))) match {
-            case Right(fd) ⇒ fd
-            case Left(e)   ⇒ throw new ConfigurationException("Could not create custom failure detector [" + fqcn + "] due to:" + e.toString)
-          }
+    val failureDetector = {
+      import clusterSettings.{ FailureDetectorImplementationClass ⇒ fqcn }
+      system.dynamicAccess.createInstanceFor[FailureDetector](
+        fqcn, Seq(classOf[ActorSystem] -> system, classOf[ClusterSettings] -> clusterSettings)).fold(
+          e ⇒ throw new ConfigurationException("Could not create custom failure detector [" + fqcn + "] due to:" + e.toString),
+          identity)
     }
 
     new Cluster(system, failureDetector)

akka-cluster/src/main/scala/akka/cluster/ClusterSettings.scala

@@ -16,10 +16,7 @@ class ClusterSettings(val config: Config, val systemName: String) {
 
   final val FailureDetectorThreshold = getDouble("akka.cluster.failure-detector.threshold")
   final val FailureDetectorMaxSampleSize = getInt("akka.cluster.failure-detector.max-sample-size")
-  final val FailureDetectorImplementationClass: Option[String] = getString("akka.cluster.failure-detector.implementation-class") match {
-    case ""   ⇒ None
-    case fqcn ⇒ Some(fqcn)
-  }
+  final val FailureDetectorImplementationClass = getString("akka.cluster.failure-detector.implementation-class")
   final val FailureDetectorMinStdDeviation: Duration =
     Duration(getMilliseconds("akka.cluster.failure-detector.min-std-deviation"), MILLISECONDS)
   final val FailureDetectorAcceptableHeartbeatPause: Duration =

akka-cluster/src/multi-jvm/scala/akka/cluster/FailureDetectorStrategy.scala

@@ -55,7 +55,7 @@ trait AccrualFailureDetectorStrategy extends FailureDetectorStrategy { self: Mul
 
   override val failureDetector: FailureDetector = new AccrualFailureDetector(system, new ClusterSettings(system.settings.config, system.name))
 
-  override def markNodeAsAvailable(address: Address): Unit = { /* no-op */ }
+  override def markNodeAsAvailable(address: Address): Unit = ()
 
-  override def markNodeAsUnavailable(address: Address): Unit = { /* no-op */ }
+  override def markNodeAsUnavailable(address: Address): Unit = ()
 }

akka-cluster/src/test/scala/akka/cluster/ClusterConfigSpec.scala

@@ -18,7 +18,7 @@ class ClusterConfigSpec extends AkkaSpec {
       import settings._
       FailureDetectorThreshold must be(8.0 plusOrMinus 0.0001)
       FailureDetectorMaxSampleSize must be(1000)
-      FailureDetectorImplementationClass must be(None)
+      FailureDetectorImplementationClass must be(classOf[AccrualFailureDetector].getName)
       FailureDetectorMinStdDeviation must be(100 millis)
       FailureDetectorAcceptableHeartbeatPause must be(3 seconds)
       NodeToJoin must be(None)