Can TeamFoundationServer's GetService ever return null?

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You've likely seen a lot of blog posts (mine included) that use the TeamFoundationServer's GetService method to get an instance of a proffered interface/service, for instance VersionControlServer (in Microsoft.TeamFoundation.VersionControl.Client):

    TeamFoundationServer tfs = TeamFoundationServerFactory.GetServer(wsInfo.ServerUri.AbsoluteUri);

    VersionControlServer vcs = (VersionControlServer)tfs.GetService(typeof(VersionControlServer));

 

The question came up internally whether it was possible to have it return null - if you're asking for one of our registered interfaces or one of our specifically supported classes (for instance, WorkItemStore, VersionControlServer), then you'll either get the instance or an exception if there's a problem.

However, and this is more trivia than anything useful, if you ask for something outside of that, you'll get null back.  Here's some PowerShell output showing that in action:

PS C:\Documents and Settings\jmanning> [reflection.Assembly]::LoadWithPartialName("Microsoft.TeamFoundation.Client")

GAC Version Location

--- ------- --------

True v2.0.50727 C:\WINDOWS\assembly\GAC_32\Microsoft.TeamFoundation.Client\8.0.0.0__b03f5f7f11d50a3a\Microsoft.TeamFoundation.Client.dll

PS C:\Documents and Settings\jmanning> $tfs = [Microsoft.TeamFoundation.Client.TeamFoundationServerFactory]::GetServer("https://tkbgitvstfat01:8080")

PS C:\Documents and Settings\jmanning> $tfs.GetService([Microsoft.TeamFoundation.VersionControl.Client.VersionControlServer]) -eq $null

False

PS C:\Documents and Settings\jmanning> $tfs.GetService([System.Collections.ArrayList]) -eq $null

True

PS C:\Documents and Settings\jmanning> $tfs.GetService([System.Collections.IList]) -eq $null

True

Here’s an exception getting thrown when we do something like pass null:

PS C:\Documents and Settings\jmanning> $tfs.GetService($null) -eq $null

Exception calling "GetService" with "1" argument(s): "Value cannot be null.

Parameter name: serviceType"

At line:1 char:16

+ $tfs.GetService( <<<< $null) -eq $null

PS C:\Documents and Settings\jmanning>