Declare method as static

CRM/CallNextActivityBlock/Utils/CallNextActivityBlock.php

@@ -17,7 +17,7 @@ class CRM_CallNextActivityBlock_Utils_CallNextActivityBlock {
    * @param int $contactId The numeric ID of the displayed Contact.
    * @param int $assigneeId The numeric ID of the Contact wanting to be assigned.
    */
-  public function get_activity($contactId, $assigneeId) {
+  public static function get_activity($contactId, $assigneeId) {
 
     try {