Year function can't handle some date string

[yuqi1129]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

Master

select year('2020|5|4|||');

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

mysql> select year('2020|5|4|||');
+---------------------+
| year('2020|5|4|||') |
+---------------------+
|                2020 |
+---------------------+
1 row in set (0.04 sec)

mysql> select version();
+------------+
| version()  |
+------------+
| 5.7.22-log |
+------------+
1 row in set (0.02 sec)

3. What did you see instead (Required)

mysql>  select year('2020|5|4|||');
ERROR 1105 (HY000): strconv.Atoi: parsing "": invalid syntax
mysql> select tidb_version();
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tidb_version()                                                                                                                                                                                                                                |
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Release Version: None
Edition: Community
Git Commit Hash: None
Git Branch: None
UTC Build Time: None
GoVersion: go1.16.4
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false |
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

4. What is your TiDB version? (Required)

Master branch