title: List only drive letters where driveletter and filesystem are not $null
body: <p>I am trying to make a list of drive letters but include only the ones which the driveletter and the filesystem are not null. An example of what I have now is</p>
  
  <pre><code>$winvolume = Get-WmiObject -computername $a -class win32_volume | Select-Object -Property driveletter, filesystem, capacity, freespace
  
  foreach ($i in $winvolume.driveletter) { 
      if ($i -ne $null){ $drive = $i + ',' + $drive } 
  }
  </code></pre>
  
  <p>this outputs the format correctly, but only checks if the driveletter is null or not, how can I also check against $winvolume.filesystem before listing these drive letters?</p>
  
  <p>Thanks!</p>