[Bug]: json_decode(): Passing null to parameter #1 ($json) of type string is deprecated at lib/private/Comments/Manager.php#95

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github OR Nextcloud Community Forum (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

Found in a log file:

url: /apps/recommendations/api/recommendations 
message: json_decode(): Passing null to parameter #1 ($json) of type string is deprecated at lib/private/Comments/Manager.php#95 
version: 29.0.3.5

https://github.com/nextcloud/server/blob/0d16ba6445d9dd3973c875ad1ffab04e970fbc06/lib/private/Comments/Manager.php#L95

https://github.com/nextcloud/server/blob/c52b7e5ebc6736de2d9991af379e4ed9885aab7b/core/Migrations/Version29000Date20231213104850.php#L40-L46

https://github.com/nextcloud/server/blob/226134a19533bf30aa3d9db30752045386a6741b/lib/private/Comments/Comment.php#L407-L418

I'm confused. The IComment object tries to decode the json when calling getMetaData, but normalizeDatabaseData already decoded it?

Steps to reproduce

No idea, found it in the customer log.

Expected behavior

Column does not allow null, but somehow we call json_decode with null.