BATCH-2283: Updated MessageChannelPartitionHandler to return null when no partitions are specified

spring-batch-integration/src/main/java/org/springframework/batch/integration/async/AsyncItemWriter.java

@@ -32,7 +32,7 @@ public class AsyncItemWriter<T> implements ItemWriter<Future<T>>, InitializingBe
 	}
 	
 	/**
-	 * @param delegate
+	 * @param delegate ItemWriter that does the actual writing of the Future results
 	 */
 	public void setDelegate(ItemWriter<T> delegate) {
 		this.delegate = delegate;

spring-batch-integration/src/main/java/org/springframework/batch/integration/launch/JobLaunchRequest.java

@@ -31,8 +31,8 @@ public class JobLaunchRequest {
 	private final JobParameters jobParameters;
 
 	/**
-	 * @param job
-	 * @param jobParameters
+	 * @param job job to be launched
+	 * @param jobParameters parameters to run the job with
 	 */
 	public JobLaunchRequest(Job job, JobParameters jobParameters) {
 		super();

spring-batch-integration/src/main/java/org/springframework/batch/integration/launch/JobLaunchingGateway.java

@@ -57,7 +57,7 @@ public class JobLaunchingGateway extends AbstractReplyProducingMessageHandler {
 	 * is a failure to start the job. The cause of the exception will be a
 	 * {@link JobExecutionException}.
 	 *
-	 * @throws MessageHandlingException
+	 * @throws MessageHandlingException when a job cannot be launched
 	 */
 	@Override
 	protected Object handleRequestMessage(Message<?> requestMessage) {

spring-batch-integration/src/main/java/org/springframework/batch/integration/launch/JobLaunchingMessageHandler.java

@@ -35,7 +35,7 @@ public class JobLaunchingMessageHandler implements JobLaunchRequestHandler {
 	private final JobLauncher jobLauncher;
 
 	/**
-	 * @param jobLauncher
+	 * @param jobLauncher {@link org.springframework.batch.core.launch.JobLauncher} used to execute Spring Batch jobs
 	 */
 	public JobLaunchingMessageHandler(JobLauncher jobLauncher) {
 		super();

spring-batch-integration/src/main/java/org/springframework/batch/integration/partition/MessageChannelPartitionHandler.java

@@ -18,6 +18,7 @@ import org.springframework.messaging.Message;
 import org.springframework.messaging.MessageChannel;
 import org.springframework.messaging.PollableChannel;
 import org.springframework.util.Assert;
+import org.springframework.util.CollectionUtils;
 
 import java.util.Collection;
 import java.util.List;
@@ -119,6 +120,11 @@ public class MessageChannelPartitionHandler implements PartitionHandler {
 			StepExecution masterStepExecution) throws Exception {
 
 		Set<StepExecution> split = stepExecutionSplitter.split(masterStepExecution, gridSize);
+
+		if(CollectionUtils.isEmpty(split)) {
+			return null;
+		}
+
 		int count = 0;
 
 		if (replyChannel == null) {