Across .NET Core 3.0 and .NET 5.0, we annotated 94% of the netcoreapp assemblies for nullable reference types. In .NET 6.0/.NET 7.0, we plan to annotate the remaining 6% of that surface area and continue through other assemblies built from the dotnet/runtime repo.

This issue represents the assemblies previously tracked in #2339 that did not get completed in .NET 5.0. Following the same practices we used in .NET 5.0, we will:

• Submit individual PRs, one for each assembly. Each PR should include changes to both the src and the ref. Each PR should contain only changes related to the nullable annotations/attributes, no other changes.
• PRs can be merged once the annotations have been appropriately reviewed in PR.
• Group all of the nullable annotation changes together in Changes to Nullable Reference Type Annotations in .NET 6.0 docs#21202

In .NET 5.0, as was tracked in #2339, we completed groups 1-8, most of group 9, all of group 10, and some items in groups 11 and 12

Planned for .NET 6.0

Group 9

• System.ComponentModel.TypeConverter (Add nullable annotations to System.ComponentModel.TypeConverter #54961 - @krwq)
• Finish System.Data.Common (Nullable annotations for the remainder of System.Data.Common #55409 - @krwq)

Group 11 (not part of netcoreapp but reference netcoreapp)

• System.DirectoryServices (Add nullable annotations to System.DirectoryServices #48454)
• System.Diagnostics.EventLog
• System.DirectoryServices.Protocols
• System.Security.Permissions
• System.Windows.Extensions Nullable annotation for System.Windows.Extensions #57896

Stretch Goal for .NET 6, or Carry Over to .NET 7.0

Group 12 (built from dotnet/runtime but not in netcoreapp and reference netstandard)

With netstandard not annotated, we will need to be cognizant of the fact that all dependencies will be viewed as oblivious:

• System.CodeDom => netstandard
• System.ComponentModel.Composition.Registration => netstandard, System.Reflection.Context
• System.Composition.AttributedModel => netstandard
• System.Composition.Convention => netstandard, System.Composition.AttributedModel
• System.Composition.Hosting => netstandard, System.Composition.Runtime
• System.Composition.Runtime => netstandard
• System.Composition.TypedParts => netstandard, System.Composition.Runtime, System.Composition.AttributedModel, System.Composition.Hosting
• System.Configuration.ConfigurationManager => netstandard, System.Security.Cryptography.ProtectedData
• System.Diagnostics.PerformanceCounter => System.Configuration.ConfigurationManager
• System.DirectoryServices.AccountManagement => System.Configuration.ConfigurationManager
• System.IO.Ports => netstandard
• System.Management => System.CodeDom
• System.Runtime.Caching => netstandard, System.Configuration.ConfigurationManager
• System.Security.Cryptography.Xml => netstandard
• System.ServiceModel.Syndication => netstandard

Lastly

• Remove #nullable enable from individual files after all dependent projects annotated