Scheduled task cleanup_invalid_scheduled_mails fails with database JSON error

[c-roos268]

Hi team,

We encountered a fatal database error when running the scheduled task for cleaning up invalid scheduled emails (mod_booking\task\cleanup_invalid_scheduled_mails).

Environment details:

Moodle version: 4.5.10 (Build: 20260216)

mod_booking version: 2026051900

Error message:

Plaintext
Error reading from database (Invalid JSON text in argument 1 to function json_extract: "The document is empty." at position 0.)

Cause:
The task uses the MySQL/MariaDB JSON_EXTRACT() function on a database column (likely within the booking tables). However, if a row contains an empty string ("" or NULL) instead of a valid JSON object ({}), the database query crashes instantly and causes the scheduled task to fail.

Suggested fix:
It would be great if the query within this task could be updated to safeguard against empty or null values. For example, by adding a condition to filter out empty rows before attempting to parse them with JSON_EXTRACT(), such as:

SQL
WHERE your_json_column IS NOT NULL AND your_json_column != '' AND your_json_column != '{}'

Could you please look into adding a fallback or validation check for empty data fields in this task so it doesn't break the cron execution?

Thank you!

[jrchamp]

It look like this specific instance is happening within the scheduledmails class.

The adhoc task custom data already has a clause to make sure it is "JSON-like", but the booking_rules.rulejson is missing that type of safety measure.

moodle-mod_booking/classes/local/scheduledmails.php

Line 92 in 6f13986

WHERE ta.customdata LIKE '{%' -- ensure JSON-like