Use a default subject if a rendered newsletter subject is empty [MAILPOET-1462]

lib/Cron/Workers/SendingQueue/Tasks/Newsletter.php

@@ -101,6 +101,11 @@ class Newsletter {
       null,
       $queue
     );
+    // if the rendered subject is empty, use a default subject,
+    // having no subject in a newsletter is considered spammy
+    if(empty(trim($queue->newsletter_rendered_subject))) {
+      $queue->newsletter_rendered_subject = __('No subject', 'mailpoet');
+    }
     $queue->newsletter_rendered_body = $rendered_newsletter;
     $queue->save();
     // catch DB errors
@@ -172,7 +177,7 @@ class Newsletter {
   function stopNewsletterPreProcessing($error_code = null) {
     MailerLog::processError(
       'queue_save',
-      __('There was an error processing your newsletter during sending. If possible, please contact us and report this issue.'),
+      __('There was an error processing your newsletter during sending. If possible, please contact us and report this issue.', 'mailpoet'),
       $error_code
     );
   }

tests/integration/Cron/Workers/SendingQueue/Tasks/NewsletterTest.php

@@ -235,6 +235,15 @@ class NewsletterTest extends \MailPoetTest {
       ->contains(date_i18n('dS', Functions::currentTime('timestamp')));
   }
 
+  function testItUsesADefaultSubjectIfRenderedSubjectIsEmptyWhenPreprocessingNewsletter() {
+    $newsletter = $this->newsletter;
+    $newsletter->subject = '  [custom_shortcode:should_render_empty]  ';
+    $queue = $this->queue;
+    $newsletter = $this->newsletter_task->preProcessNewsletter($newsletter, $queue);
+    $queue = SendingTask::getByNewsletterId($newsletter->id);
+    expect($queue->newsletter_rendered_subject)
+      ->equals('No subject');
+  }
 
   function testItUsesRenderedNewsletterBodyAndSubjectFromQueueObjectWhenPreparingNewsletterForSending() {
     $queue = $this->queue;