Get-wbsummary FOReach

Hi, please help! i'm sooo close!
i run a FOREACH on the function below against 4 servers.  if one of the servers is offline i only get 3 results back, how do i make it spit out a row indicating 'Command Failed' or 'Server unavailable' for the 4th server? 

what i get now is an html table with:
PSComputerName  LastBackupTime           LastBackupResultDetailedHR
server1                 6/18/2014 1:30:05 AM      0
server2                 6/18/2014 1:00:14 AM      0
server4                 6/17/2014 9:30:31 PM      0

And what i want is an html table with:

PSComputerName  LastBackupTime           LastBackupResultDetailedHR
server1                 6/18/2014 1:30:05 AM      0
server2                 6/18/2014 1:00:14 AM      0
server3                 NO RESPONSE or Command Failed
server4                 6/17/2014 9:30:31 PM      0

_____________________________________________________________________
function Get-WBStats
{
BEGIN {}
Process
{
Invoke-Command -ScriptBlock {
                                get-wbsummary
                            } -computername $Servername -credential $Cred | select PSComputerName,LastBackupTime,LastbackupResultDetailedHR | sort pscomputername                           
}
END {}
}

Thank you, any help is appreciated.

MN