fix: workflows, exception when running a step with a null workflow state

sdk/java-sdk-protobuf/src/main/scala/kalix/javasdk/impl/workflow/WorkflowImpl.scala

@@ -306,8 +306,10 @@ final class WorkflowImpl(system: ActorSystem, val services: Map[String, Workflow
           val timerScheduler = new TimerSchedulerImpl(service.messageCodec, system)
           val stepResponse =
             try {
-              val decoded = service.messageCodec.decodeMessage(executeStep.userState.get)
-              router._internalSetInitState(decoded, false) // here we know that workflow is still running
+              executeStep.userState.foreach { state =>
+                val decoded = service.messageCodec.decodeMessage(state)
+                router._internalSetInitState(decoded, finished = false) // here we know that workflow is still running
+              }
               router._internalHandleStep(
                 executeStep.commandId,
                 executeStep.input,

sdk/java-sdk-spring/src/it/java/com/example/wiring/workflowentities/SpringWorkflowIntegrationTest.java

@@ -459,6 +459,26 @@ public void shouldNotUpdateWorkflowStateAfterEndTransition() {
     assertThat(execute(componentClient.forWorkflow(workflowId).call(DummyWorkflow::get))).isEqualTo(10);
   }
 
+  @Test
+  public void shouldRunWorkflowStepWithoutInitialState() {
+    //given
+    var workflowId = randomId();
+
+    //when
+    String response = execute(componentClient.forWorkflow(workflowId)
+        .call(WorkflowWithoutInitialState::start));
+
+    assertThat(response).contains("ok");
+
+    //then
+    await()
+        .atMost(10, TimeUnit.of(SECONDS))
+        .untilAsserted(() -> {
+          var state = execute(componentClient.forWorkflow(workflowId).call(WorkflowWithoutInitialState::get));
+          assertThat(state).contains("success");
+        });
+  }
+
   private <T> T execute(DeferredCall<Any, T> deferredCall) {
     return execute(deferredCall, timeout);
   }

sdk/java-sdk-spring/src/it/java/com/example/wiring/workflowentities/WorkflowWithoutInitialState.java

@@ -0,0 +1,65 @@
+/*
+ * Copyright 2021 Lightbend Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.example.wiring.workflowentities;
+
+import kalix.javasdk.annotations.Id;
+import kalix.javasdk.annotations.TypeId;
+import kalix.javasdk.client.ComponentClient;
+import kalix.javasdk.workflow.Workflow;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.PutMapping;
+import org.springframework.web.bind.annotation.RequestMapping;
+
+import java.util.concurrent.CompletableFuture;
+
+@Id("id")
+@TypeId("workflow-without-initial-state")
+@RequestMapping("/workflow-without-initial-state/{id}")
+public class WorkflowWithoutInitialState extends Workflow<String> {
+
+
+  private ComponentClient componentClient;
+
+  public WorkflowWithoutInitialState(ComponentClient componentClient) {
+    this.componentClient = componentClient;
+  }
+
+  @Override
+  public WorkflowDef<String> definition() {
+    var test =
+        step("test")
+            .asyncCall(() -> CompletableFuture.completedFuture("ok"))
+            .andThen(String.class, result -> effects().updateState("success").end());
+
+    return workflow()
+        .addStep(test);
+  }
+
+  @PutMapping()
+  public Effect<String> start() {
+    return effects().transitionTo("test").thenReply("ok");
+  }
+
+  @GetMapping()
+  public Effect<String> get() {
+    if (currentState() == null) {
+      return effects().reply("empty");
+    } else {
+      return effects().reply(currentState());
+    }
+  }
+}