User Profile Application: SynchronizeMIIS encounters an exception: System.NullReferenceException: Object reference not set to an instance of an object

What this means is that we’re getting a null reference exception, when the FIM management agent/connector for SharePoint finishes up. It calls a finalize method that’s part of the web service (http://sp:27741/_vti_bin/ProfileImportExportService.asmx:FinalizeProfileImportExportProcess ) that the FIM MA for SP uses. This finalize method is checking for a running instance of the User Profile ADImport Timer Job. The problem is that this timer job only gets created if your UPSA is set to use the “Active Directory Import” setting. If you never use/set that setting, which you probably don’t because you’re trying to use your External FIM deployment, the Timer Job will never exist. To create the timer job, all you need to do is change the setting in your UPSA’s “Configure Synchronization Settings” page to “Active Directory Import” and then to External FIM. This won’t break anything. You can also leverage the following PowerShell.

$upsa = Get-SPServiceApplication -name "YOUR_UPSA_NAME"
$upsa.NoILMUsed = $true
$upsa.Update()
$upsa.NoILMUsed = $false
$upsa.Update()

You might need to restart the User Profile Sync service, then run your full sync again