框架依赖内容需要设置为可空

如果不是可空导入无法还原

https://github.com/dotnet-campus/SourceYard/issues/87#issuecomment-961786363

build/Version.props

 <Project>
   <PropertyGroup>
-    <Version>0.1.19393-alpha04</Version>
+    <Version>0.1.19393-alpha05</Version>
   </PropertyGroup>
 </Project>

sample/App/TheLib/TheLib.csproj

@@ -6,7 +6,7 @@
   </PropertyGroup>
 
    <ItemGroup> 
-     <PackageReference Include="dotnetCampus.SourceYard" Version="0.1.19393-alpha04"> 
+     <PackageReference Include="dotnetCampus.SourceYard" Version="0.1.19393-alpha05"> 
        <PrivateAssets>all</PrivateAssets> 
        <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets> 
      </PackageReference> 

src/dotnetCampus.SourceYard/PackFlow/NuspecFiles/NuspecContexts/NuspecMetadata.cs

@@ -26,7 +26,7 @@ namespace dotnetCampus.SourceYard.PackFlow.NuspecFiles.NuspecContexts
 
         [XmlArray(elementName: "frameworkAssemblies", Namespace = "")]
         [XmlArrayItem(elementName: "frameworkAssembly")]
-        public List<NuspecFrameworkAssembly> FrameworkAssemblies { set; get; } = new List<NuspecFrameworkAssembly>();
+        public List<NuspecFrameworkAssembly>? FrameworkAssemblies { set; get; }
 
         [XmlElement("id")] 
         public string? Id { get; set; }