diff --git a/lib/form/autocomplete.php b/lib/form/autocomplete.php
index 2be3c40cde5..3d05905f86f 100644
--- a/lib/form/autocomplete.php
+++ b/lib/form/autocomplete.php
@@ -204,7 +204,7 @@ class MoodleQuickForm_autocomplete extends MoodleQuickForm_select {
             // Normally this is cleaned as a side effect of it not being a valid option,
             // but in this case we need to detect and skip it manually.
             if ($value === '_qf__force_multiselect_submission' || $value === null) {
-                $value = '';
+                $value = $this->getMultiple() ? [] : '';
             }
             return $this->_prepareValue($value, $assoc);
         } else {
diff --git a/lib/form/select.php b/lib/form/select.php
index 9e052dacc40..b84b37a6bd2 100644
--- a/lib/form/select.php
+++ b/lib/form/select.php
@@ -166,8 +166,9 @@ class MoodleQuickForm_select extends HTML_QuickForm_select implements templatabl
     */
     function exportValue(&$submitValues, $assoc = false)
     {
+        $emptyvalue = $this->getMultiple() ? [] : '';
         if (empty($this->_options)) {
-            return $this->_prepareValue(null, $assoc);
+            return $this->_prepareValue($emptyvalue, $assoc);
         }
 
         $value = $this->_findValue($submitValues);
@@ -187,7 +188,7 @@ class MoodleQuickForm_select extends HTML_QuickForm_select implements templatabl
         }
 
         if (empty($cleaned)) {
-            return $this->_prepareValue(null, $assoc);
+            return $this->_prepareValue($emptyvalue, $assoc);
         }
         if ($this->getMultiple()) {
             return $this->_prepareValue($cleaned, $assoc);
@@ -223,6 +224,7 @@ class MoodleQuickForm_select extends HTML_QuickForm_select implements templatabl
             $options[] = $o;
         }
         $context['options'] = $options;
+        $context['nameraw'] = $this->getName();
 
         return $context;
     }
diff --git a/lib/form/tags.php b/lib/form/tags.php
index ef3719f9433..28468134ac0 100644
--- a/lib/form/tags.php
+++ b/lib/form/tags.php
@@ -261,7 +261,6 @@ class MoodleQuickForm_tags extends MoodleQuickForm_autocomplete {
             $url = new moodle_url('/tag/manage.php', array('tc' => $this->get_tag_collection()));
             $context['managestandardtagsurl'] = $url->out(false);
         }
-        $context['nameraw'] = $this->getName();
 
         return $context;
     }
diff --git a/lib/form/tests/autocomplete_test.php b/lib/form/tests/autocomplete_test.php
index 17b9c61b7c7..a3b3cf88513 100644
--- a/lib/form/tests/autocomplete_test.php
+++ b/lib/form/tests/autocomplete_test.php
@@ -49,7 +49,7 @@ class core_form_autocomplete_testcase extends basic_testcase {
         $submission = array('testel' => 2);
         $this->assertEquals($element->exportValue($submission), 2);
         $submission = array('testel' => 3);
-        $this->assertNull($element->exportValue($submission));
+        $this->assertEquals('', $element->exportValue($submission));
 
         // A select with multiple values validates the data.
         $options = array('1' => 'One', 2 => 'Two');
@@ -61,6 +61,18 @@ class core_form_autocomplete_testcase extends basic_testcase {
         $element = new MoodleQuickForm_autocomplete('testel', null, array(), array('multiple'=>'multiple', 'ajax'=>'anything'));
         $submission = array('testel' => array(2, 3));
         $this->assertEquals($element->exportValue($submission), array(2, 3));
+
+        // A select with single value without anything selected.
+        $options = array('1' => 'One', 2 => 'Two');
+        $element = new MoodleQuickForm_autocomplete('testel', null, $options);
+        $submission = array();
+        $this->assertEquals('', $element->exportValue($submission));
+
+        // A select with multiple values without anything selected.
+        $options = array('1' => 'One', 2 => 'Two');
+        $element = new MoodleQuickForm_autocomplete('testel', null, $options, array('multiple' => 'multiple'));
+        $submission = array();
+        $this->assertEquals([], $element->exportValue($submission));
     }
 
 }
diff --git a/theme/boost/templates/core_form/element-autocomplete-inline.mustache b/theme/boost/templates/core_form/element-autocomplete-inline.mustache
index bc7434a19b3..175280ea15b 100644
--- a/theme/boost/templates/core_form/element-autocomplete-inline.mustache
+++ b/theme/boost/templates/core_form/element-autocomplete-inline.mustache
@@ -1,6 +1,9 @@
 {{< core_form/element-template-inline }}
     {{$element}}
         {{^element.frozen}}
+        {{#element.multiple}}
+            <input type="hidden" name="{{element.nameraw}}" value="_qf__force_multiselect_submission">
+        {{/element.multiple}}
         <select class="custom-select {{#error}}is-invalid{{/error}}" name="{{element.name}}"
             id="{{element.id}}"
             {{#element.multiple}}multiple{{/element.multiple}}
diff --git a/theme/boost/templates/core_form/element-autocomplete.mustache b/theme/boost/templates/core_form/element-autocomplete.mustache
index a7fea2cc3c5..8736f0a720a 100644
--- a/theme/boost/templates/core_form/element-autocomplete.mustache
+++ b/theme/boost/templates/core_form/element-autocomplete.mustache
@@ -1,6 +1,9 @@
 {{< core_form/element-template }}
     {{$element}}
         {{^element.frozen}}
+        {{#element.multiple}}
+            <input type="hidden" name="{{element.nameraw}}" value="_qf__force_multiselect_submission">
+        {{/element.multiple}}
         <select class="custom-select {{#error}}is-invalid{{/error}}" name="{{element.name}}"
             id="{{element.id}}"
             {{#element.multiple}}multiple{{/element.multiple}}
diff --git a/theme/boost/templates/core_form/element-select-inline.mustache b/theme/boost/templates/core_form/element-select-inline.mustache
index 5af56848f47..bd5ae84fb1d 100644
--- a/theme/boost/templates/core_form/element-select-inline.mustache
+++ b/theme/boost/templates/core_form/element-select-inline.mustache
@@ -1,6 +1,9 @@
 {{< core_form/element-template-inline }}
     {{$element}}
         {{^element.frozen}}
+        {{#element.multiple}}
+            <input type="hidden" name="{{element.nameraw}}" value="_qf__force_multiselect_submission">
+        {{/element.multiple}}
     <select class="{{^element.multiple}}custom-select{{/element.multiple}}
                    {{#element.multiple}}form-control{{/element.multiple}}
                    {{#error}}is-invalid{{/error}}"
diff --git a/theme/boost/templates/core_form/element-select.mustache b/theme/boost/templates/core_form/element-select.mustache
index 66c6db5fdc6..49664083597 100644
--- a/theme/boost/templates/core_form/element-select.mustache
+++ b/theme/boost/templates/core_form/element-select.mustache
@@ -21,6 +21,7 @@
 
     Context variables required for this template:
     * id - Element id,
+    * nameraw - Raw Element name without '[]'
     * name - Element name,
     * label -  Element label,
     * multiple - multi select?,
@@ -49,6 +50,7 @@
     {
         "element": {
             "id": "id_maildisplay",
+            "nameraw": "maildisplay",
             "name": "maildisplay",
             "label": null,
             "multiple": null,
@@ -92,6 +94,9 @@
 {{< core_form/element-template }}
     {{$element}}
         {{^element.frozen}}
+        {{#element.multiple}}
+            <input type="hidden" name="{{element.nameraw}}" value="_qf__force_multiselect_submission">
+        {{/element.multiple}}
         <select class="{{^element.multiple}}custom-select{{/element.multiple}}
                        {{#element.multiple}}form-control{{/element.multiple}}
                        {{#error}}is-invalid{{/error}}"