fix count on null

app/Libs/Metrics/MyMetricProvider.php

@@ -77,7 +77,10 @@ class MyMetricProvider implements ProviderInterface
 
             foreach ($mailboxes as $account)
             {
-                $countOfEmailAliases += count($account->getAliases());
+                $emailAliases = $account->getAliases();
+                if (isset($emailAliases) && is_countable($emailAliases)) {
+                    $countOfEmailAliases += count($account->getAliases());
+                }
             }
 
             $domainAliases = $this->getDomainAliases($domainName);