Generic .nuspec file

Hey guys,
I created a build project that uses a generic .nuspec file with variables inside.
Everything goes fine until i get to the files section.
The files section looks like this:

<files>
        <file src="..\..\build\Compile\Host.exe"/>
        <file src="..\..\build\Compile\*.dll"/>
        <file src="..\..\build\Compile\*.config"/>
        <file src="..\..\build\Compile\assets\**\*.*" target="assets"/>
</files>

The thing is that some of the projects has all of those files included and it works fine, but some of the projects has no "assets" folder within, and the packing job is not working.

Is there any way to tell the "nuget pack" command to just continue even if not all of the files are there, and he packs whatever he finds?
So i will not have to create 2 .nuspec files.

Thanks.

Product: ProGet
Version: 3.5.4

You may be best asking this on NuGet forums, as this relates to behavior in the nuget.exe client. We do not use "nuget.exe pack" ourselves (instead, we opt to use the proget client tools) as it's more reliable and has defined behaviors.