diff --git a/mod/workshop/db/install.xml b/mod/workshop/db/install.xml
index d3ffcffcb7f..d9e72cf0e73 100644
--- a/mod/workshop/db/install.xml
+++ b/mod/workshop/db/install.xml
@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8" ?>
-<XMLDB PATH="mod/workshop/db" VERSION="20180626" COMMENT="XMLDB file for Moodle mod/workshop"
+<XMLDB PATH="mod/workshop/db" VERSION="20210302" COMMENT="XMLDB file for Moodle mod/workshop"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:noNamespaceSchemaLocation="../../../lib/xmldb/xmldb.xsd"
 >
@@ -109,7 +109,7 @@
         <FIELD NAME="assessmentid" TYPE="int" LENGTH="10" NOTNULL="true" SEQUENCE="false" COMMENT="Part of which assessment this grade is of"/>
         <FIELD NAME="strategy" TYPE="char" LENGTH="30" NOTNULL="true" SEQUENCE="false"/>
         <FIELD NAME="dimensionid" TYPE="int" LENGTH="10" NOTNULL="true" SEQUENCE="false" COMMENT="Foreign key. References dimension id in one of the grading strategy tables."/>
-        <FIELD NAME="grade" TYPE="number" LENGTH="10" NOTNULL="true" SEQUENCE="false" DECIMALS="5" COMMENT="Given grade in the referenced assessment dimension."/>
+        <FIELD NAME="grade" TYPE="number" LENGTH="10" NOTNULL="false" SEQUENCE="false" DECIMALS="5" COMMENT="Given grade in the referenced assessment dimension."/>
         <FIELD NAME="peercomment" TYPE="text" NOTNULL="false" SEQUENCE="false" COMMENT="Reviewer's comment to the grade value."/>
         <FIELD NAME="peercommentformat" TYPE="int" LENGTH="3" NOTNULL="false" DEFAULT="0" SEQUENCE="false" COMMENT="The format of peercomment field"/>
       </FIELDS>
diff --git a/mod/workshop/db/upgrade.php b/mod/workshop/db/upgrade.php
index 0ae1705d925..a41cfe36bb4 100644
--- a/mod/workshop/db/upgrade.php
+++ b/mod/workshop/db/upgrade.php
@@ -98,5 +98,18 @@ function xmldb_workshop_upgrade($oldversion) {
     // Automatically generated Moodle v3.10.0 release upgrade line.
     // Put any upgrade step following this.
 
+    if ($oldversion < 2020110901) {
+
+        // Changing nullability of field grade on table workshop_grades to null.
+        $table = new xmldb_table('workshop_grades');
+        $field = new xmldb_field('grade', XMLDB_TYPE_NUMBER, '10, 5', null, null, null, null, 'dimensionid');
+
+        // Launch change of nullability for field grade.
+        $dbman->change_field_notnull($table, $field);
+
+        // Main savepoint reached.
+        upgrade_mod_savepoint(true, 2020110901, 'workshop');
+    }
+
     return true;
 }
diff --git a/mod/workshop/form/accumulative/assessment_form.php b/mod/workshop/form/accumulative/assessment_form.php
index 95f6132f6d3..12ae8b4890e 100644
--- a/mod/workshop/form/accumulative/assessment_form.php
+++ b/mod/workshop/form/accumulative/assessment_form.php
@@ -76,11 +76,13 @@ class workshop_accumulative_assessment_form extends workshop_assessment_form {
 
             // grade for this aspect
             $label = get_string('dimensiongradefor', 'workshopform_accumulative', $dimtitle);
-            $options = make_grades_menu($fields->{'grade__idx_' . $i});
-            $options = array('-1' => get_string('choosedots')) + $options;
-            $mform->addElement('select', 'grade__idx_' . $i, $label, $options);
-            $mform->addRule(array('grade__idx_' . $i, 'minusone') , get_string('mustchoosegrade', 'workshopform_accumulative'), 'compare', 'gt');
-
+            if ($fields->{'grade__idx_' . $i}) {
+                $options = make_grades_menu($fields->{'grade__idx_' . $i});
+                $options = array('-1' => get_string('choosedots')) + $options;
+                $mform->addElement('select', 'grade__idx_' . $i, $label, $options);
+                $mform->addRule(array('grade__idx_' . $i, 'minusone'),
+                    get_string('mustchoosegrade', 'workshopform_accumulative'), 'compare', 'gt');
+            }
             // comment
             $label = get_string('dimensioncommentfor', 'workshopform_accumulative', $dimtitle);
             //$mform->addElement('editor', 'peercomment__idx_' . $i, $label, null, array('maxfiles' => 0));
diff --git a/mod/workshop/form/accumulative/lib.php b/mod/workshop/form/accumulative/lib.php
index 87a5f99c30c..bac0ec60250 100644
--- a/mod/workshop/form/accumulative/lib.php
+++ b/mod/workshop/form/accumulative/lib.php
@@ -269,7 +269,9 @@ class workshop_accumulative_strategy implements workshop_strategy {
             $grade->assessmentid = $assessment->id;
             $grade->strategy = 'accumulative';
             $grade->dimensionid = $data->{'dimensionid__idx_' . $i};
-            $grade->grade = $data->{'grade__idx_' . $i};
+            if (isset($data->{'grade__idx_' . $i})) {
+                $grade->grade = $data->{'grade__idx_' . $i};
+            }
             $grade->peercomment = $data->{'peercomment__idx_' . $i};
             $grade->peercommentformat = FORMAT_MOODLE;
             if (empty($grade->id)) {
diff --git a/mod/workshop/version.php b/mod/workshop/version.php
index 02b9c4851a3..45f4acaad65 100644
--- a/mod/workshop/version.php
+++ b/mod/workshop/version.php
@@ -24,6 +24,6 @@
 
 defined('MOODLE_INTERNAL') || die();
 
-$plugin->version   = 2020110900;        // The current module version (YYYYMMDDXX)
+$plugin->version   = 2020110901;        // The current module version (YYYYMMDDXX).
 $plugin->requires  = 2020110300;        // Requires this Moodle version.
 $plugin->component = 'mod_workshop';