diff --git a/dm/config/task.go b/dm/config/task.go
index 6bb649ded9..ff90b842dd 100644
--- a/dm/config/task.go
+++ b/dm/config/task.go
@@ -827,5 +827,8 @@ func AdjustTargetDBTimeZone(config *DBConfig) {
 			return
 		}
 	}
+	if config.Session == nil {
+		config.Session = make(map[string]string, 1)
+	}
 	config.Session["time_zone"] = defaultTimeZone
 }
diff --git a/tests/all_mode/data/db2.prepare.sql b/tests/all_mode/data/db2.prepare.sql
index 10199a4381..fc8900ae73 100644
--- a/tests/all_mode/data/db2.prepare.sql
+++ b/tests/all_mode/data/db2.prepare.sql
@@ -6,8 +6,7 @@ create table t2 (
     name varchar(20),
     ts timestamp,
     PRIMARY KEY (id));;
-insert into t2 (name, ts) values ('Arya', now()), ('Bran', '2021-05-11 10:01:05');
-insert into t2 (name) values ('Sansa');
+insert into t2 (name, ts) values ('Arya', now()), ('Bran', '2021-05-11 10:01:05'), ('Sansa', NULL);
 
 -- test block-allow-list
 drop database if exists `ignore_db`;