`DATE_FORMAT` is not compatible with MySQL for empty foramt

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)

### 2. What did you expect to see? (Required)

```
mysql> SELECT DATE_FORMAT('2023-10-30', '');
+-------------------------------+
| DATE_FORMAT('2023-10-30', '') |
+-------------------------------+
| NULL |
+-------------------------------+
1 row in set (0.01 sec)
```

### 3. What did you see instead (Required)

```
mysql> SELECT DATE_FORMAT('2023-10-30', '');
+-------------------------------+
| DATE_FORMAT('2023-10-30', '') |
+-------------------------------+
| |
+-------------------------------+
1 row in set (0.01 sec)
```

### 4. What is your TiDB version? (Required)