PHP 8.3 TypeError in date element: get_date_format_string() argument #2 must be of type string, null given

[Trarco]

A TypeError is thrown when rendering a Custom Certificate using the Date element. This occurs because the $dateformat property is null, but the helper method expects a mandatory string. This is particularly prevalent in PHP 8.x environments.

Environment

• Moodle Version: 4.5.8
• PHP Version: 8.3.6

Error Details / Stack Trace

Exception - mod_customcert\element_helper::get_date_format_string(): Argument #2 ($dateformat) must be of type string, null given, called in [dirroot]/mod/customcert/element/date/classes/element.php on line 269

Stack trace:
line 749 of /mod/customcert/classes/element_helper.php: TypeError thrown
line 269 of /mod/customcert/element/date/classes/element.php: call to mod_customcert\element_helper::get_date_format_string()
line 143 of /mod/customcert/rearrange.php: call to customcertelement_date\element->render_html()

Steps to Reproduce

1. Use Moodle 4.5+ with PHP 8.3.
2. Create or edit a Custom Certificate.
3. Access the Rearrange elements page (rearrange.php).
4. Add or view a "Date" element
5. Set the date format (example used: "6 July 2026")
6. Save or attempt to view the certificate
7. The page fails to load with the TypeError.

[Trarco]

I have identified that the root cause seems to be related to the rearrange elements functionality. It appears that when saving the positions of elements, the plugin occasionally mismatches or overwrites element IDs/data.

The Issue: During the drag-and-drop or saving process in rearrange.php, the data associated with a date element is being replaced or corrupted by data from another element (specifically observed with userfield with custom userfield).

Behavior: This behavior seems random.

Impact: Because a userfield element does not have a dateformat property, the date element's configuration becomes null. Under PHP 8.3, this immediately triggers the TypeError mentioned above, effectively locking the user out of the certificate editor since the "Rearrange" and "Edit" pages can no longer render the corrupted element.

[mdjnelson]

Thanks for the report @Trarco? Does this happen after using the modal to make changes, cause there was a recent-ish issue I fixed regarding this.