Short circuit when ItemGroup is epty

Directory.Build.targets

@@ -111,15 +111,6 @@
     <Compile Include="$(SharedSourceRoot)ReferenceAssemblyInfo.cs" LinkBase="Properties" />
   </ItemGroup>
 
-  <ItemGroup>
-    <!-- Workaround when there is no vNext SDK available, copy known apphost/framework reference info from 3.0 -->
-    <KnownFrameworkReference
-      Include="@(KnownFrameworkReference->WithMetadataValue('TargetFramework', 'netcoreapp3.0'))"
-      TargetFramework="$(DefaultNetCoreTargetFramework)"
-      Condition="!(@(KnownFrameworkReference->AnyHaveMetadataValue('TargetFramework', '$(DefaultNetCoreTargetFramework)')))"
-      />
-  </ItemGroup>
-
   <ItemGroup>
     <KnownFrameworkReference Update="Microsoft.NETCore.App">
       <!-- Always update the 'latest version', whether the repo is servicing or not. -->

eng/Workarounds.targets

@@ -1,11 +1,15 @@
 <!-- Use this file to workaround issues. List the issue tracking the item to fix so we can remove the workaround when the issue is resolved. -->
 <Project>
+
+  <PropertyGroup>
+    <NETCoreAppMaximumVersion>5.0</NETCoreAppMaximumVersion>
+  </PropertyGroup>
   <!--
     Workaround https://github.com/aspnet/AspNetCore/issues/4257.
     The web sdk adds an implicit framework reference. This removes it until we can update our build to use framework references.
   -->
   <ItemGroup>
-    <FrameworkReference Remove="Microsoft.AspNetCore.App" />
+    <KnownFrameworkReference Remove="Microsoft.AspNetCore.App" />
     <!-- Required because the Razor SDK will generate attributes -->
     <Reference Include="Microsoft.AspNetCore.Mvc" Condition="'$(UsingMicrosoftNETSdkWeb)' == 'true' AND '$(TargetFrameworkIdentifier)' == '.NETCoreApp' AND '$(GenerateRazorAssemblyInfo)' == 'true'" />
   </ItemGroup>
@@ -25,6 +29,20 @@
     <PackageReference Include="Internal.AspNetCore.BuildTasks" PrivateAssets="All" Version="$(InternalAspNetCoreBuildTasksPackageVersion)" IsImplicitlyDefined="true" />
   </ItemGroup>
 
+  <ItemGroup>
+    <!-- Workaround when there is no vNext SDK available, copy known apphost/framework reference info from 3.0 -->
+    <KnownAppHostPack 
+      Include="@(KnownAppHostPack->WithMetadataValue('TargetFramework', 'netcoreapp3.0'))"
+      TargetFramework="$(DefaultNetCoreTargetFramework)"
+      Condition="(@(KnownAppHostPack->Count()) != '0') AND (!(@(KnownAppHostPack->AnyHaveMetadataValue('TargetFramework', '$(DefaultNetCoreTargetFramework)'))))"
+      />
+    <KnownFrameworkReference
+      Include="@(KnownFrameworkReference->WithMetadataValue('TargetFramework', 'netcoreapp3.0'))"
+      TargetFramework="$(DefaultNetCoreTargetFramework)"
+      Condition="(@(KnownFrameworkReference->Count()) != '0') AND (!(@(KnownFrameworkReference->AnyHaveMetadataValue('TargetFramework', '$(DefaultNetCoreTargetFramework)'))))"
+      />
+  </ItemGroup>
+
   <!-- Workaround for netstandard2.1 projects until we can get a preview 8 SDK containing https://github.com/dotnet/sdk/pull/3463 fix. -->
   <ItemGroup>
     <KnownFrameworkReference Update="NETStandard.Library">