title: Cannot extract the contents of a TGZ file using F# and SharpZipLib
body: <p>I am learning F# and Deedle.  I am trying to extract the contents of this <a href="https://ddragon.leagueoflegends.com/cdn/dragontail-12.4.1.tgz" rel="nofollow noreferrer">TGZ File</a> using SharpZipLib.  I downloaded the TGZ to my local drive.  I think I am close because out1 works, but out2 errs.  I am sure the code could be written better with pipe forwarding or composition, but it first needs to work.  Does anyone have any ideas?</p>
  <pre><code>open ICSharpCode.SharpZipLib.GZip
  open  ICSharpCode.SharpZipLib.Tar
  
  let extract path filename =
      let fullpath = Path.Combine(path, filename)
      let inSt = File.OpenRead(fullpath)
      let gSt = new GZipInputStream(inSt)
      let tar = TarArchive.CreateOutputTarArchive(gSt)
      let out1 = tar.ListContents
      let out2 = tar.ExtractContents(path)
      out2
      
  extract &quot;C:/Downloads/&quot; &quot;dragontail-12.4.1.tgz&quot;
  </code></pre>
  <p>This is the error:</p>
  <pre><code>Error: System.NullReferenceException: Object reference not set to an instance of an object.
     at ICSharpCode.SharpZipLib.Tar.TarArchive.ExtractContents(String destinationDirectory, Boolean allowParentTraversal) in /_/src/ICSharpCode.SharpZipLib/Tar/TarArchive.cs:line 620
     at ICSharpCode.SharpZipLib.Tar.TarArchive.ExtractContents(String destinationDirectory) in /_/src/ICSharpCode.SharpZipLib/Tar/TarArchive.cs:line 600
     at FSI_0104.extract(String path, String filename)
     at &lt;StartupCode$FSI_0104&gt;.$FSI_0104.main@()
  </code></pre>