Fix crashing page due to newsletter not found error

MAILPOET-4688

mailpoet/assets/js/src/newsletters/campaign_stats/page.tsx

@@ -99,6 +99,10 @@ function CampaignStatsPageComponent({ match, history, location }: Props) {
     );
   }
 
+  if (!newsletter) {
+    return <h3> {MailPoet.I18n.t('emailDoesNotExist')} </h3>;
+  }
+
   return (
     <>
       <HideScreenOptions />

mailpoet/views/newsletters.html

@@ -194,6 +194,8 @@
     'checkBackInHours': __('Nice job! Check back in %1$d hour(s) for more stats.'),
     'improveThisLinkText': __('What can I do to improve this?'),
 
+    'emailDoesNotExist': __('This email does not exist.'),
+
     'templateFileMalformedError': __('This template file appears to be damaged. Please try another one.'),
     'importTemplateTitle': __('Import a template'),
     'selectJsonFileToUpload': __('Select a .json file to upload'),