Add a lazy instantiation of Mailer in NewSubscriberNofiticationMailer

[MAILPOET-1823]

lib/Subscribers/NewSubscriberNotificationMailer.php

@@ -3,6 +3,7 @@
 namespace MailPoet\Subscribers;
 
 use MailPoet\Config\Renderer;
+use MailPoet\Mailer\Mailer;
 use MailPoet\Models\Segment;
 use MailPoet\Models\Subscriber;
 use MailPoet\WP\Functions;
@@ -43,11 +44,7 @@ class NewSubscriberNotificationMailer {
     } else {
       $this->wordpress_functions = new Functions();
     }
-    if ($mailer) {
     $this->mailer = $mailer;
-    } else {
-      $this->mailer = new \MailPoet\Mailer\Mailer(false, $this->constructSenderEmail());
-    }
     $this->settings = new SettingsController();
   }
 
@@ -63,8 +60,9 @@ class NewSubscriberNotificationMailer {
       return;
     }
     try {
-      $this->mailer->getSenderNameAndAddress($this->constructSenderEmail());
+
-      $this->mailer->send($this->constructNewsletter($subscriber, $segments), $settings['address']);
+      $this->getMailer()->getSenderNameAndAddress($this->constructSenderEmail());
+      $this->getMailer()->send($this->constructNewsletter($subscriber, $segments), $settings['address']);
     } catch (\Exception $e) {
       if (WP_DEBUG) {
         throw $e;
@@ -88,6 +86,16 @@ class NewSubscriberNotificationMailer {
     return !(bool)$settings['enabled'];
   }
 
+  /**
+   * @return Mailer
+   */
+  private function getMailer() {
+    if (!$this->mailer) {
+      $this->mailer = new Mailer(false, $this->constructSenderEmail());
+    }
+    return $this->mailer;
+  }
+
   private function constructSenderEmail() {
     $url_parts = parse_url($this->wordpress_functions->homeUrl());
     $site_name = strtolower($url_parts['host']);