fix empty upstreamTaskCodes (#8405)

Co-authored-by: caishunfeng <534328519@qq.com>

dolphinscheduler-api/src/main/java/org/apache/dolphinscheduler/api/service/impl/TaskDefinitionServiceImpl.java

@@ -54,6 +54,7 @@ import org.apache.commons.lang3.StringUtils;
 
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collections;
 import java.util.Date;
 import java.util.HashMap;
 import java.util.List;
@@ -272,6 +273,7 @@ public class TaskDefinitionServiceImpl extends BaseServiceImpl implements TaskDe
     /**
      * delete task definition
      * Only offline and no downstream dependency can be deleted
+     *
      * @param loginUser login user
      * @param projectCode project code
      * @param taskCode task code
@@ -449,7 +451,10 @@ public class TaskDefinitionServiceImpl extends BaseServiceImpl implements TaskDe
         }
         List<ProcessTaskRelation> upstreamTaskRelations = processTaskRelationMapper.queryUpstreamByCode(projectCode, taskCode);
         Set<Long> upstreamCodeSet = upstreamTaskRelations.stream().map(ProcessTaskRelation::getPreTaskCode).collect(Collectors.toSet());
-        Set<Long> upstreamTaskCodes = Arrays.stream(upstreamCodes.split(Constants.COMMA)).map(Long::parseLong).collect(Collectors.toSet());
+        Set<Long> upstreamTaskCodes = Collections.emptySet();
+        if (StringUtils.isNotEmpty(upstreamCodes)) {
+            upstreamTaskCodes = Arrays.stream(upstreamCodes.split(Constants.COMMA)).map(Long::parseLong).collect(Collectors.toSet());
+        }
         if (CollectionUtils.isEqualCollection(upstreamCodeSet, upstreamTaskCodes) && taskDefinitionToUpdate == null) {
             putMsg(result, Status.SUCCESS);
             return result;