fix: System.NullReferenceException on Undo

[workgroupengineering]

fixes #425

[workgroupengineering]

Do I need to make any other changes? I hope the merge and release takes place soon.

[danipen]

LGTM

[danipen]

It seems that the Azure Pipelines task Pack AvaloniaEdit is failing in a consistent way. Any ideas?

##[warning].NET 5 has some compatibility issues with older Nuget versions(<=5.7), so if you are using an older Nuget version(and not dotnet cli) to restore, then the dotnet cli commands (e.g. dotnet build) which rely on such restored packages might fail. To mitigate such error, you can either: (1) - Use dotnet cli to restore, (2) - Use Nuget version 5.8 to restore, (3) - Use global.json using an older sdk version(<=3) to build
##[error]Error: The process 'C:\Program Files\dotnet\dotnet.exe' failed with exit code 1
##[error]An error occurred while trying to pack the files.
Info: Azure Pipelines hosted agents have been updated and now contain .Net 5.x SDK/Runtime along with the older .Net Core version which are currently lts. Unless you have locked down a SDK version for your project(s), 5.x SDK might be picked up which might have breaking behavior as compared to previous versions. You can learn more about the breaking changes here: https://docs.microsoft.com/en-us/dotnet/core/tools/ and https://docs.microsoft.com/en-us/dotnet/core/compatibility/ . To learn about more such changes and troubleshoot, refer here: https://docs.microsoft.com/en-us/azure/devops/pipelines/tasks/build/dotnet-core-cli?view=azure-devops#troubleshooting
Finishing: Pack AvaloniaEdit

Any ideas?

[workgroupengineering]

I see. Net standard 2.0 does not support Clamp. I fix it tomorrow.