Merge pull request #18637 from demeritcowboy/no-details

#2075 - E_NOTICE viewing an activity that has no details contents

CRM/Activity/Form/Activity.php

@@ -503,7 +503,7 @@ class CRM_Activity_Form_Activity extends CRM_Contact_Form_Task {
     }
 
     if ($this->_action & CRM_Core_Action::VIEW) {
-      $this->_values['details'] = CRM_Utils_String::purifyHtml($this->_values['details']);
+      $this->_values['details'] = CRM_Utils_String::purifyHtml($this->_values['details'] ?? '');
       $url = CRM_Utils_System::url(implode("/", $this->urlPath), "reset=1&id={$this->_activityId}&action=view&cid={$this->_values['source_contact_id']}");
       CRM_Utils_Recent::add(CRM_Utils_Array::value('subject', $this->_values, ts('(no subject)')),
         $url,