Logging email fails array to string conversion

Array to string conversion fails at class Email.php line 2087.
The _logDelivery function under Email.php is trying to convert an array to a string and it's failing as expected.

src/Mailer/Email.php

@@ -2060,7 +2060,8 @@ public function send($content = null)
 
         return $contents;
     }
-
+
+
     /**
      * Log the email message delivery.
      *
@@ -2084,10 +2085,20 @@ protected function _logDelivery($contents)
         }
         Log::write(
             $config['level'],
-            PHP_EOL . $contents['headers'] . PHP_EOL . PHP_EOL . $contents['message'],
+            PHP_EOL . $this->_isKeyArray($contents['headers']) . PHP_EOL . PHP_EOL . $this->_isKeyArray($contents['message']),
             $config['scope']
         );
     }
+
+
+    /**
+     * @param null $key
+     * @return null|string
+     */
+    private function _isKeyArray($key = null)
+    {
+        return is_array($key) ? implode(';', $key) : $key;
+    }
 
     /**
      * Static method to fast create an instance of \Cake\Mailer\Email