Issue #3278727 by DieterHolvoet, moshe weitzman: During install: Invalid...

Issue #3278727 by DieterHolvoet, moshe weitzman: During install: Invalid argument supplied for foreach() mailchimp_transactional.install:62

mailchimp_transactional.install

@@ -45,43 +45,54 @@ function mailchimp_transactional_install() {
     $mailsystem_config = \Drupal::configFactory()->getEditable('mailsystem.settings');
     $default_sender = $mailsystem_config->get('defaults.sender');
     $default_formatter = $mailsystem_config->get('defaults.formatter');
+    $changed = FALSE;
 
     if ($default_sender == 'mandrill_mail') {
       $mailsystem_config->set('defaults.sender', 'mailchimp_transactional_mail');
+      $changed = TRUE;
     }
     elseif ($default_sender == 'mandrill_test_mail') {
       $mailsystem_config->set('defaults.sender', 'mailchimp_transactional_test_mail');
+      $changed = TRUE;
     }
 
     if ($default_formatter == 'mandrill_mail') {
       $mailsystem_config->set('defaults.formatter', 'mailchimp_transactional_mail');
+      $changed = TRUE;
     }
     elseif ($default_formatter == 'mandrill_test_mail') {
       $mailsystem_config->set('defaults.formatter', 'mailchimp_transactional_test_mail',);
+      $changed = TRUE;
     }
-    foreach ($mailsystem_config->get('modules') as $module => $keys) {
+    foreach ($mailsystem_config->get('modules') ?? [] as $module => $keys) {
       foreach ($keys as $key => $plugins) {
         $sender_key = 'modules.' . $module . '.' . $key . '.sender';
         $sender = $mailsystem_config->get($sender_key);
         if ($sender == 'mandrill_mail') {
           $mailsystem_config->set($sender_key, 'mailchimp_transactional_mail');
+          $changed = TRUE;
         }
         elseif ($sender == 'mandrill_test_mail') {
           $mailsystem_config->set($sender_key, 'mailchimp_transactional_test_mail');
+          $changed = TRUE;
         }
 
         $formatter_key = 'modules.' . $module . '.' . $key . '.formatter';
         $formatter = $mailsystem_config->get($formatter_key);
         if ($formatter == 'mandrill_mail') {
           $mailsystem_config->set($formatter_key, 'mailchimp_transactional_mail');
+          $changed = TRUE;
         }
         elseif ($formatter == 'mandrill_test_mail') {
-          $mailsystem_config->set($formatter_key, 'mailchimp_transactional_test_mail',);
+          $mailsystem_config->set($formatter_key, 'mailchimp_transactional_test_mail');
+          $changed = TRUE;
         }
       }
     }
-    $mailsystem_config->save();
 
+    if ($changed) {
+      $mailsystem_config->save();
+    }
   }
   else {
     // Set default values for config which require dynamic values.