fix: Exception on loop after agent call

Signed-off-by: Matheus Andre <matheusandr2@gmail>

Author: Matheus Andre

experimental/lambda/src/main/java/io/serverlessworkflow/impl/executors/func/JavaForExecutorBuilder.java

@@ -69,7 +69,7 @@ protected WorkflowValueResolver<Collection<?>> buildCollectionFilter() {
   }
 
   private Object collectionFilterObject(ForTaskFunction taskFunctions) {
-    return taskFunctions.getForClass().isPresent()
+    return taskFunctions.getForClass() != null && taskFunctions.getForClass().isPresent()
         ? new TypedFunction(
             taskFunctions.getCollection(), taskFunctions.getForClass().orElseThrow())
         : taskFunctions.getCollection();

experimental/lambda/src/test/java/io/serverless/workflow/impl/executors/func/ForTaskFunctionRegressionTest.java

@@ -0,0 +1,60 @@
+/*
+ * Copyright 2020-Present The Serverless Workflow Specification Authors
+ *
+ * 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 io.serverless.workflow.impl.executors.func;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import io.serverlessworkflow.api.types.Workflow;
+import io.serverlessworkflow.api.types.func.ForTaskFunction;
+import io.serverlessworkflow.fluent.func.FuncWorkflowBuilder;
+import io.serverlessworkflow.impl.WorkflowApplication;
+import java.util.Collection;
+import java.util.List;
+import java.util.concurrent.ExecutionException;
+import org.junit.jupiter.api.Test;
+
+class ForTaskFunctionRegressionTest {
+
+  @Test
+  void initializesOptionalFieldsAsEmpty() {
+    ForTaskFunction taskFunction = new ForTaskFunction();
+
+    assertThat(taskFunction.getWhileClass()).isNotNull().isEmpty();
+    assertThat(taskFunction.getItemClass()).isNotNull().isEmpty();
+    assertThat(taskFunction.getForClass()).isNotNull().isEmpty();
+  }
+
+  @Test
+  void forLoopWithoutExplicitCollectionClassExecutesSuccessfully()
+      throws InterruptedException, ExecutionException {
+    try (WorkflowApplication app = WorkflowApplication.builder().build()) {
+      Workflow workflow =
+          FuncWorkflowBuilder.workflow("loop-without-collection-class")
+              .tasks(
+                  tasks ->
+                      tasks.forEach(
+                          f ->
+                              f.whileC(CallTest::isEven)
+                                  .collection(v -> (Collection<?>) v)
+                                  .tasks(CallTest::sum)))
+              .build();
+
+      var result = app.workflowDefinition(workflow).instance(List.of(2, 4, 6)).start().get();
+
+      assertThat(result.asNumber().orElseThrow()).isEqualTo(12);
+    }
+  }
+}

experimental/types/src/main/java/io/serverlessworkflow/api/types/func/ForTaskFunction.java

@@ -24,9 +24,9 @@ public class ForTaskFunction extends ForTask {
 
   private static final long serialVersionUID = 1L;
   private LoopPredicateIndexFilter<?, ?> whilePredicate;
-  private Optional<Class<?>> whileClass;
-  private Optional<Class<?>> itemClass;
-  private Optional<Class<?>> forClass;
+  private Optional<Class<?>> whileClass = Optional.empty();
+  private Optional<Class<?>> itemClass = Optional.empty();
+  private Optional<Class<?>> forClass = Optional.empty();
   private Function<?, Collection<?>> collection;
 
   public <T, V> ForTaskFunction withWhile(LoopPredicate<T, V> whilePredicate) {