[Bug-11101] fix task failover NPE (#11168)

(cherry picked from commit 6c7e00c4aa)

dolphinscheduler-master/src/main/java/org/apache/dolphinscheduler/server/master/service/MasterFailoverService.java

@@ -40,6 +40,7 @@ import org.apache.dolphinscheduler.server.master.runner.task.TaskProcessorFactor
 import org.apache.dolphinscheduler.server.utils.ProcessUtils;
 import org.apache.dolphinscheduler.service.process.ProcessService;
 import org.apache.dolphinscheduler.service.registry.RegistryClient;
+import org.apache.dolphinscheduler.spi.utils.StringUtils;
 
 import org.apache.commons.collections4.CollectionUtils;
 import org.apache.commons.lang3.time.StopWatch;
@@ -232,6 +233,20 @@ public class MasterFailoverService {
             // kill worker task, When the master failover and worker failover happened in the same time,
             // the task may not be failover if we don't set NEED_FAULT_TOLERANCE.
             // This can be improved if we can load all task when cache a workflowInstance in memory
+            sendKillCommandToWorker(taskInstance);
+        } else {
+            LOGGER.info("The failover taskInstance is a master task");
+        }
+
+        taskInstance.setState(ExecutionStatus.NEED_FAULT_TOLERANCE);
+        taskInstance.setFlag(Flag.NO);
+        processService.saveTaskInstance(taskInstance);
+    }
+
+    private void sendKillCommandToWorker(@NonNull TaskInstance taskInstance) {
+        if (StringUtils.isEmpty(taskInstance.getHost())) {
+            return;
+        }
         try {
             TaskKillRequestCommand killCommand = new TaskKillRequestCommand(taskInstance.getId());
             Host workerHost = Host.of(taskInstance.getHost());
@@ -240,13 +255,6 @@ public class MasterFailoverService {
         } catch (ExecuteException e) {
             LOGGER.error("Kill task failed", e);
         }
-        } else {
-            LOGGER.info("The failover taskInstance is a master task");
-        }
-
-        taskInstance.setState(ExecutionStatus.NEED_FAULT_TOLERANCE);
-        taskInstance.setFlag(Flag.NO);
-        processService.saveTaskInstance(taskInstance);
     }
 
     private boolean checkTaskInstanceNeedFailover(@NonNull TaskInstance taskInstance) {