XML : Powershell: Format XML returns empty

I am trying to use powershell to format a messy xml file to a file with indentation where every tag starts on a new line.

The input file looks like:

  <?xml version="1.0" encoding="WINDOWS-1252"?>  <RESULT>  <HEADER><ACCOUNT>035574623593</ACCOUNT><DATE_FROM>20150101</DATE_FROM><DATE_TO>20150526</DATE_TO><DATE_EQUAL></DATE_EQUAL><HD_DATIN>2015-11-27 15:16:52</HD_DATIN><HD_START>2015-11-27 15:16:52</HD_START><HD_ENGINE>WCV00228</HD_ENGINE><HD_QUERYID>984</HD_QUERYID></HEADER>  <FOOTER><FT_STATUS>NF</FT_STATUS><FT_RECORDS>2</FT_RECORDS><FT_SIZE>282</FT_SIZE><FT_ORDER>1</FT_ORDER><FT_STOP>2015-11-27 15:16:53</FT_STOP></FOOTER>  </RESULT>    

This is a piece of my code where the formatting takes place:

  function Format-XML {Param ([string]$xmlfile)    $Doc=New-Object system.xml.xmlDataDocument    $doc.Load($xmlfile)    $sw=New-Object system.io.stringwriter    $settings= New-Object System.Xml.XmlWriterSettings    $settings.NewLineOnAttributes = $false    $settings.Indent = 1    $settings.NewLineOnAttributes = $true    $writer=[system.xml.XmlWriter]::Create($sw, $settings)    $doc.WriteContentTo($writer)    $sw.ToString()    }    Format-XML ("${app}se-xf-out\UH99DEFI.BEMVS000.U$datum.T$counter") > "${app}se-xf-out\UH99DEFI.BEMVS001.U$datum.T$counter"    

Can someone help me? The output file is empty (but still 1kb)