Fixed #4076

CHANGELOG-v3.md

@@ -19,6 +19,7 @@
 - Fixed a SQL error that could occur when using the Asset Indexes utility, if any filenames contained 4+ byte characters.
 - Fixed a bug where entry queries could return duplicate results for any entries that belong to a section that has soft-deleted structures associated with it. ([#4066](https://github.com/craftcms/cms/issues/4066))
 - Fixed a bug where rebuilding project config would not work with Matrix fields with no block types. ([#4074](https://github.com/craftcms/cms/issues/4074)
+- Fixed an error that occurred when sending emails if the `testToEmailAddress` config setting was set. ([#4076](https://github.com/craftcms/cms/issues/4076))
 
 ## 3.1.20.1 - 2019-03-27
 

src/mail/Message.php

@@ -118,11 +118,15 @@ public function setBcc($bcc)
     // =========================================================================
 
     /**
-     * @param string|array|User|User[] $emails
+     * @param string|array|User|User[]|null $emails
      * @return string|array
      */
     private function _normalizeEmails($emails)
     {
+        if (empty($emails)) {
+            return null;
+        }
+
         if (!is_array($emails)) {
             $emails = [$emails];
         }