Check the credentials returned to see if they are null.
The answer is a bit tricky due to the use case for the CmdLet. The following is the best you can do in this case.
Try{
if($cred = Get-Credential -Credential $cred -ErrorAction Stop){
Write-Host good
Write-Host $cred.Username
}else{
Write-Host no creds
}
}
Catch{
Write-Host no creds
}
\_(ツ)_/