fix: rubocop offenses

app/mailers/application_mailer.rb

@@ -1,4 +1,4 @@
 class ApplicationMailer < ActionMailer::Base
-  default from: ENV['SMTP_DEFAULT_FROM']
+  default from: ENV.fetch('SMTP_DEFAULT_FROM', '[email protected]')
   layout 'mailer'
 end

config/initializers/mailjet.rb

@@ -2,5 +2,5 @@
 Mailjet.configure do |config|
   config.api_key = ENV['SMTP_API_KEY']
   config.secret_key = ENV['SMTP_API_SECRET']
-  config.default_from = ENV['SMTP_DEFAULT_FROM']
+  config.default_from = ENV.fetch('SMTP_DEFAULT_FROM', '[email protected]')
 end

spec/mailers/data_download_mailer_spec.rb

@@ -10,15 +10,15 @@
         surname: 'surname',
         location: 'location',
         organisation: 'organisation',
-        purposes: ['purpose1', 'purpose2']
+        purposes: %w[purpose1 purpose2]
       }
     }
     let(:mail) { DataDownloadMailer.send_download_file_info_email data }
 
     it 'renders the headers' do
       expect(mail.subject).to eq('TPI data has been downloaded')
       expect(mail.to).to eq(['[email protected]'])
-      expect(mail.from).to eq([ENV['SMTP_DEFAULT_FROM']].reject(&:blank?))
+      expect(mail.from).to eq([ENV.fetch('SMTP_DEFAULT_FROM', '[email protected]')])
 
       expect(mail.body.encoded).to include('[email protected]')
       expect(mail.body.encoded).to include('job_title')