Error occurs when you start adding the cohort_sync enrol metod, and click the Cancel button without filing up the form.

Our environment:

Nginx, PHP 7.3, Postgres 11.

To reproduce.

1. Create at least one system cohort.
2. Create course
3. Enter the Course
4. Click participants
5. Under the cog click Enrolment methods
6. Choose Cohort sync in Add method dropdown
7. Click Cancel 

After that you got the error:

 
Error reading from database

More information about this error
×Debug info: BŁĄD: invalid input syntax for integer: ""
SELECT * FROM mdl_cohort WHERE id = $1 ORDER BY name
– line 1500 of /lib/dml/moodle_database.php: call to pgsql_native_moodle_database->get_records_sql()
– line 603 of /lib/pear/HTML/QuickForm/select.php: call to MoodleQuickForm_cohort->setValue()
– line 230 of /lib/form/autocomplete.php: call to HTML_QuickForm_select->onQuickFormEvent()
– line 2071 of /lib/formslib.php: call to MoodleQuickForm_autocomplete->onQuickFormEvent()
– line 324 of /lib/formslib.php: call to MoodleQuickForm->updateSubmission()
– line 228 of /lib/formslib.php: call to moodleform->_process_submission()
– line 69 of /enrol/editinstance.php: call to moodleform->__construct()
[array (
0 => '',
)]
Error code: dmlreadexception
×Stack trace: * line 486 of /lib/dml/moodle_database.php: dml_read_exception thrown

• line 329 of /lib/dml/pgsql_native_moodle_database.php: call to moodle_database->query_end()
• line 920 of /lib/dml/pgsql_native_moodle_database.php: call to pgsql_native_moodle_database->query_end()
• line 1500 of /lib/dml/moodle_database.php: call to pgsql_native_moodle_database->get_records_sql()
• line 136 of /lib/form/cohort.php: call to moodle_database->get_records_select()
• line 603 of /lib/pear/HTML/QuickForm/select.php: call to MoodleQuickForm_cohort->setValue()
• line 230 of /lib/form/autocomplete.php: call to HTML_QuickForm_select->onQuickFormEvent()
• line 2071 of /lib/formslib.php: call to MoodleQuickForm_autocomplete->onQuickFormEvent()
• line 324 of /lib/formslib.php: call to MoodleQuickForm->updateSubmission()
• line 228 of /lib/formslib.php: call to moodleform->_process_submission()
• line 69 of /enrol/editinstance.php: call to moodleform->__construct()