How to exclude all content files?

With NuGet 4.6.2, how to exclude all content files when creating the package from a project file using PackageReference?

I run this command as postbuid event :

$(SolutionDir)\.nuget\nuget pack $(ProjectPath) -IncludeReferencedProjects -properties Configuration=$(ConfigurationName) -symbols

I tried this nuspec file :

<package><metadata><id>$id$</id><version>$version$</version><title>$title$</title><authors>$author$</authors><owners>$author$</owners><requireLicenseAcceptance>false</requireLicenseAcceptance><description>$description$</description><releaseNotes></releaseNotes><copyright>$copyright$</copyright><tags></tags><contentFiles><files include="**\*.*" exclude="**\*.*" /></contentFiles></metadata><files><file src="**\*.*" target="content" exclude="**\*.*" /></files></package>

But content files are always in the package