Polish JobLauncherCommandLineRunner

The JobLauncherCommandLineRunner reassigned method arguments inside the
merge method. Instead of reassigning the method argument just return
the new instance directly.

Also some minor cleanup (unnesseccary null check and continue keyword).

Closes gh-10612

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/batch/JobLauncherCommandLineRunner.java

@@ -181,8 +181,7 @@ public class JobLauncherCommandLineRunner
 		Map<String, JobParameter> merged = new HashMap<String, JobParameter>();
 		merged.putAll(parameters.getParameters());
 		merged.putAll(additionals);
-		parameters = new JobParameters(merged);
-		return parameters;
+		return new JobParameters(merged);
 	}
 
 	private void executeRegisteredJobs(JobParameters jobParameters)
@@ -199,7 +198,6 @@ public class JobLauncherCommandLineRunner
 				}
 				catch (NoSuchJobException ex) {
 					logger.debug("No job found in registry for job name: " + jobName);
-					continue;
 				}
 			}
 		}
@@ -210,11 +208,9 @@ public class JobLauncherCommandLineRunner
 			JobInstanceAlreadyCompleteException, JobParametersInvalidException,
 			JobParametersNotFoundException {
 		JobParameters nextParameters = getNextJobParameters(job, jobParameters);
-		if (nextParameters != null) {
-			JobExecution execution = this.jobLauncher.run(job, nextParameters);
-			if (this.publisher != null) {
-				this.publisher.publishEvent(new JobExecutionEvent(execution));
-			}
+		JobExecution execution = this.jobLauncher.run(job, nextParameters);
+		if (this.publisher != null) {
+			this.publisher.publishEvent(new JobExecutionEvent(execution));
 		}
 	}