Add exception

Author: narendravaghela

src/Mailer/Transport/SendGridTransport.php

@@ -193,10 +193,9 @@ protected function _prepareEmailAddresses(Message $message)
         if (!empty($replyTo)) {
             if (key($replyTo) != $replyTo[key($replyTo)]) {
                 $this->_reqParams['reply_to'] = (object)['email' => key($replyTo), 'name' => $replyTo[key($replyTo)]];
-                
             } else {
                 $this->_reqParams['reply_to'] = (object)['email' => key($replyTo)];
-            }        
+            }
         }
 
         $emails = [];
@@ -207,6 +206,10 @@ protected function _prepareEmailAddresses(Message $message)
             ];
         }
 
+        if (empty($emails['to'])) {
+            throw new SendGridApiException('Missing to email address.');
+        }
+
         foreach ($message->getCc() as $ccEmail => $ccName) {
             $emails['cc'][] = [
                 'email' => $ccEmail,