add ActorRef.noSender() for the Java API, see #3429

- Actor.noSender is not accessible from Java, but it was in 2.1 so don’t
  remove
- replaced all “null” in doc tests with ActorRef.noSender()

akka-docs/rst/java/code/docs/io/japi/EchoServer.java

@@ -24,8 +24,8 @@ public class EchoServer {
       final ActorRef watcher = system.actorOf(Props.create(Watcher.class, latch), "watcher");
       final ActorRef nackServer = system.actorOf(Props.create(EchoManager.class, EchoHandler.class), "nack");
       final ActorRef ackServer = system.actorOf(Props.create(EchoManager.class, SimpleEchoHandler.class), "ack");
-      watcher.tell(nackServer, null);
-      watcher.tell(ackServer, null);
+      watcher.tell(nackServer, ActorRef.noSender());
+      watcher.tell(ackServer, ActorRef.noSender());
       latch.await(10, TimeUnit.MINUTES);
     } finally {
       system.shutdown();

akka-docs/rst/java/code/docs/io/japi/MessageStage.java

@@ -95,7 +95,7 @@ public class MessageStage extends
             if (cmd instanceof PipelineTest.SetTarget) {
               target = ((PipelineTest.SetTarget) cmd).getRef();
             } else if (cmd instanceof TickGenerator.Tick && target != null) {
-              target.tell(cmd, null);
+              target.tell(cmd, ActorRef.noSender());
             }
             //#omitted
             if (cmd instanceof TickGenerator.Tick) {

akka-docs/rst/java/code/docs/io/japi/PipelineTest.java

@@ -72,12 +72,12 @@ public class PipelineTest {
 
           @Override
           public void onCommand(ByteString cmd) throws Throwable {
-            commandHandler.tell(cmd, null);
+            commandHandler.tell(cmd, ActorRef.noSender());
           }
 
           @Override
           public void onEvent(Message evt) throws Throwable {
-            eventHandler.tell(evt, null);
+            eventHandler.tell(evt, ActorRef.noSender());
           }
         };
         
@@ -127,9 +127,9 @@ public class PipelineTest {
         final ActorRef proc = system.actorOf(Props.create(
             P.class, this, getRef(), getRef()), "processor");
         expectMsgClass(TickGenerator.Tick.class);
-        proc.tell(msg, null);
+        proc.tell(msg, ActorRef.noSender());
         final ByteString encoded = expectMsgClass(ByteString.class);
-        proc.tell(encoded, null);
+        proc.tell(encoded, ActorRef.noSender());
         final Message decoded = expectMsgClass(Message.class);
         assert msg == decoded;
 
@@ -140,13 +140,13 @@ public class PipelineTest {
             expectMsgClass(TickGenerator.Tick.class);
           }
         };
-        proc.tell("fail!", null);
+        proc.tell("fail!", ActorRef.noSender());
         new Within(Duration.create(1700, TimeUnit.MILLISECONDS),
             Duration.create(3, TimeUnit.SECONDS)) {
           protected void run() {
             expectMsgClass(TickGenerator.Tick.class);
             expectMsgClass(TickGenerator.Tick.class);
-            proc.tell(PoisonPill.getInstance(), null);
+            proc.tell(PoisonPill.getInstance(), ActorRef.noSender());
             expectNoMsg();
           }
         };

akka-docs/rst/java/code/docs/io/japi/TickGenerator.java

@@ -9,6 +9,7 @@ import java.util.Collections;
 import scala.concurrent.duration.Deadline;
 import scala.concurrent.duration.FiniteDuration;
 import scala.util.Either;
+import akka.actor.ActorRef;
 import akka.actor.ActorSystem;
 import akka.io.AbstractPipePair;
 import akka.io.PipePair;
@@ -74,7 +75,8 @@ public class TickGenerator<Cmd, Evt> extends
           @Override
           public Iterable<Either<Evt, Cmd>> onManagementCommand(Object cmd) {
             if (cmd == trigger) {
-              ctx.getContext().self().tell(new Tick(Deadline.now().time()), null);
+              ctx.getContext().self().tell(new Tick(Deadline.now().time()),
+                  ActorRef.noSender());
               schedule();
             }
             return Collections.emptyList();