Error after updating to the newest version

Kia Ora,

We notice The calendar is now not working since the update. We have tried the purge all but still not working.

Please can you have a look, a little star comes up but not the booking.

Howdy!

WordPress has a built-in feature that detects when a plugin or theme causes a fatal error on your site, and notifies you with this automated email.

In this case, WordPress caught an error with one of your plugins, Calendar.

First, visit your website (https://doublerum.co.nz/) and check for any visible issues. Next, visit the page where the error was caught (https://doublerum.co.nz/wp-admin/admin.php?page=calendar) and check for any visible issues.

Please contact your host for assistance with investigating this issue further.

If your site appears broken and you can't access your dashboard normally, WordPress now has a special "recovery mode". This lets you safely login to your dashboard and investigate further.

When seeking help with this issue, you may be asked for some of the following information:
WordPress version 6.5.5
Active theme: Twenty Seventeen (version 3.2) Current plugin: Calendar (version 1.3.15) PHP version 8.3.8

Error Details
=============
An error of type E_ERROR was caused in line 1031 of the file /home/travelde/doublerum.co.nz/wp-content/plugins/calendar/calendar.php. Error message: Uncaught Error: Attempt to assign property "event_title" on null in /home/travelde/doublerum.co.nz/wp-content/plugins/calendar/calendar.php:1031
Stack trace:
#0 /home/travelde/doublerum.co.nz/wp-includes/class-wp-hook.php(324): calendar_edit()
#1 /home/travelde/doublerum.co.nz/wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters()
#2 /home/travelde/doublerum.co.nz/wp-includes/plugin.php(517): WP_Hook->do_action()
#3 /home/travelde/doublerum.co.nz/wp-admin/admin.php(259): do_action()
#4 {main}
? thrown

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