Fixed issue with mailing group type and multiple,

CHANGELOG.md

 Version 1.14 (under development)
 ============
 
+Version 1.13.1
+============
+
+* Fixed issue with mailing group type and multiple,
+
 Version 1.13
 ============
 

Civi/FormProcessor/Type/MailingGroupType.php

@@ -22,7 +22,7 @@ class MailingGroupType extends AbstractType implements OptionListInterface {
    * @return bool
    */
   public function isMultiple() {
-    return FALSE;
+    return $this->configuration->get('multiple') == 1 ? TRUE : FALSE;
   }
 
   /**

Civi/FormProcessor/Type/ParticipantStatusType.php

@@ -22,7 +22,7 @@ class ParticipantStatusType extends AbstractType implements OptionListInterface
    * @return bool
    */
   public function isMultiple() {
-    return FALSE;
+    return $this->configuration->get('multiple') == 1 ? TRUE : FALSE;
   }
 
   /**

Civi/FormProcessor/Type/WeekDays.php

@@ -20,7 +20,7 @@ class WeekDays extends AbstractType implements OptionListInterface {
    * @return bool
    */
   public function isMultiple() {
-    return FALSE;
+    return $this->configuration->get('multiple') == 1 ? TRUE : FALSE;
   }
 
   /**

info.xml

@@ -17,7 +17,7 @@
     <url desc="Action-Provider Extension">https://lab.civicrm.org/extensions/action-provider</url>
   </urls>
   <releaseDate>2020-09-16</releaseDate>
-  <version>1.14-dev</version>
+  <version>1.13.1</version>
   <develStage>stable</develStage>
   <compatibility>
     <ver>4.7</ver>