Host.ResolveParameterValue() throws ArgumentNullException (VS2010)

I am using VS 2010 SP1 (10.0.40219.1 SP1Rel).

The MSDN page here: http://msdn.microsoft.com/en-us/library/gg586944.aspx under the section "Obtaining arguments from TextTemplate.exe"

And the MSDN page here: http://msdn.microsoft.com/en-us/library/bb126245.aspx under the section detailing the "-a" parameter

Both indicate that Host.ResolveParameterValue(string, string, string) can be called like:

Host.ResolveParameterValue("","","argName")

However, running withing VS2010 (by saving changes to a .tt file) or by running command line (C:\...\TextTemplating\10.0\TextTransform.exe) throws the error:

RunningTransformation: System.ArgumentNullException: Value cannot be null.
Parameter name: directiveId
Server stack trace:
  at Microsoft.VisualStudio.TextTemplating.VSHost.TextTemplatingService.ResolveParameterValue(String directiveId, String processorName, String parameterName)

Is this a bug, or the expected behavior? Thanks for any help!