remove no useful code (#8552)

Co-authored-by: ywang46 <ywang46@paypal.com>

dolphinscheduler-master/src/main/java/org/apache/dolphinscheduler/server/master/runner/MasterSchedulerService.java

@@ -179,10 +179,6 @@ public class MasterSchedulerService extends Thread {
     }
 
     private List<ProcessInstance> command2ProcessInstance(List<Command> commands) {
-        if (CollectionUtils.isEmpty(commands)) {
-            return null;
-        }
-
         List<ProcessInstance> processInstances = new ArrayList<>(commands.size());
         CountDownLatch latch = new CountDownLatch(commands.size());
         for (final Command command : commands) {