The result of json_length(cast(1 as json), null) isn't same as mysql

[SeaRise]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

select json_length(1, null);

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

+------------------------------------+
| json_length(cast(1 as json), null) |
+------------------------------------+
|                               NULL |
+------------------------------------+

3. What did you see instead (Required)

+------------------------------------+
| json_length(cast(1 as json), null) |
+------------------------------------+
|                                  1 |
+------------------------------------+

4. What is your TiDB version? (Required)

Git Commit Hash: c0476a0

[SeaRise]

/sig compute

[ti-chi-bot]

@SeaRise: The label(s) sig/compute cannot be applied, because the repository doesn't have them.

In response to this:

/sig compute

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.

[SeaRise]

/sig execution

[SeaRise]

/severity minor

[SeaRise]

The result of tikv is same as mysql