I have a simple project used in a more complex solution;

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>net6.0</TargetFramework>
    <AppendTargetFrameworkToOutputPath>false</AppendTargetFrameworkToOutputPath>
    <AppendRuntimeIdentifierToOutputPath>false</AppendRuntimeIdentifierToOutputPath>
    <TrimUnusedDependencies>true</TrimUnusedDependencies>
    <BuildDependsOn>AfterClean</BuildDependsOn>
    <FileVersion>4.2.0</FileVersion>
    <Company>mycomp</Company>
    <Product>test</Product>
    <Copyright>Copyright �  2020</Copyright>
    <OutputPath>....bin</OutputPath>
  </PropertyGroup>
  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|AnyCPU'">
    <NoWarn>1701;1702;1705;NU1603;RT0099</NoWarn>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Polly" Version="[7.2.3]" />
  </ItemGroup>
</Project>

I use msbuild to restore packages and build the solution:

msbuild test.sln "/property:Platform=Any CPU" "/property:Configuration=Release" /target:restore;build /p:RestorePackagesWithLockFile=true /p:RestoreLockedMode=true /p:RestoreForceEvaluate=true /verbosity:normal

and get the following packages.lock.json file generated:

{
  "version": 1,
  "dependencies": {
    "net6.0": {
      "Polly": {
        "type": "Direct",
        "requested": "[7.2.3, 7.2.3]",
        "resolved": "7.2.3",
        "contentHash": "DeCY0OFbNdNxsjntr1gTXHJ5pKUwYzp04Er2LLeN3g6pWhffsGuKVfMBLe1lw7x76HrPkLxKEFxBlpRxS2nDEQ=="
      }
    },
**"net6.0/win-x64": {}**
  }
}

on next build with /p:RestoreForceEvaluate=false I get the following error:

test.csproj : error NU1004: The project’s runtime identifiers have changed from. Project’s runtime identifiers: , lock file’s runtime identifiers win-x64.The packages lock file is inco
nsistent with the project dependencies so restore can’t be run in locked mode. Disable the RestoreLockedMode MSBuild property or pass an explicit –force-evaluate
option to run restore to update the lock file.

If I remove entry “,
** “net6.0/win-x64″: {}**” the second restore works without error;

Any hint on why this empty entry is added to “packages.lock.json” file?

adding an extra “dummy” reference to the project
e.g.

<PackageReference Include="System.Runtime.Serialization.Primitives" Version="[4.3.0]" />

will fix the problem, because it will be added to the
“net6.0/win-x64” entry from “packages.lock.json” file.