diff --git a/classes/structure.php b/classes/structure.php
index d70347f..bd03cee 100644
--- a/classes/structure.php
+++ b/classes/structure.php
@@ -534,6 +534,9 @@ class mod_attendance_structure {
             $sess->rotateqrcode = 0;
             $sess->rotateqrcodesecret = '';
         }
+        if (!isset($sess->automarkcmid)) {
+            $sess->automarkcmid = null;
+        }
         $event->add_record_snapshot('attendance_sessions', $sess);
         $event->trigger();
 
diff --git a/db/install.xml b/db/install.xml
index 8a0f170..7aba70a 100755
--- a/db/install.xml
+++ b/db/install.xml
@@ -52,7 +52,7 @@
         <FIELD NAME="includeqrcode" TYPE="int" LENGTH="1" NOTNULL="true" DEFAULT="0" SEQUENCE="false" COMMENT="Include a QR code image when displaying the password"/>
         <FIELD NAME="rotateqrcode" TYPE="int" LENGTH="1" NOTNULL="true" DEFAULT="0" SEQUENCE="false"/>
         <FIELD NAME="rotateqrcodesecret" TYPE="char" LENGTH="10" NOTNULL="false" SEQUENCE="false"/>
-        <FIELD NAME="automarkcmid" TYPE="int" LENGTH="10" NOTNULL="true" DEFAULT="0" SEQUENCE="false"/>
+        <FIELD NAME="automarkcmid" TYPE="int" LENGTH="10" NOTNULL="false" DEFAULT="0" SEQUENCE="false"/>
       </FIELDS>
       <KEYS>
         <KEY NAME="primary" TYPE="primary" FIELDS="id" COMMENT="Primary key for attendance_sessions"/>
diff --git a/db/upgrade.php b/db/upgrade.php
index 5ea87d9..c8974b2 100755
--- a/db/upgrade.php
+++ b/db/upgrade.php
@@ -654,7 +654,7 @@ function xmldb_attendance_upgrade($oldversion=0) {
 
         // Changing precision of field statusset on table attendance_log to (1333).
         $table = new xmldb_table('attendance_sessions');
-        $field = new xmldb_field('automarkcmid', XMLDB_TYPE_CHAR, '10', null, null, null, null, 'rotateqrcodesecret');
+        $field = new xmldb_field('automarkcmid', XMLDB_TYPE_CHAR, '10', null, false, null, null, 'rotateqrcodesecret');
 
         // Launch change of precision for field statusset.
         if (!$dbman->field_exists($table, $field)) {