Fixup null annotations on ClaimsPrincipal

Author: vcsjones

src/libraries/System.Security.Claims/ref/System.Security.Claims.cs

@@ -90,7 +90,7 @@ protected ClaimsPrincipal(System.Runtime.Serialization.SerializationInfo info, S
         public ClaimsPrincipal(System.Security.Principal.IIdentity identity) { }
         public ClaimsPrincipal(System.Security.Principal.IPrincipal principal) { }
         public virtual System.Collections.Generic.IEnumerable<System.Security.Claims.Claim> Claims { get { throw null; } }
-        public static System.Func<System.Security.Claims.ClaimsPrincipal> ClaimsPrincipalSelector { get { throw null; } set { } }
+        public static System.Func<System.Security.Claims.ClaimsPrincipal?>? ClaimsPrincipalSelector { get { throw null; } set { } }
         public static System.Security.Claims.ClaimsPrincipal? Current { get { throw null; } }
         protected virtual byte[]? CustomSerializationData { get { throw null; } }
         public virtual System.Collections.Generic.IEnumerable<System.Security.Claims.ClaimsIdentity> Identities { get { throw null; } }

src/libraries/System.Security.Claims/src/System/Security/Claims/ClaimsPrincipal.cs

@@ -28,7 +28,7 @@ private enum SerializationMask
         private readonly byte[]? _userSerializationData;
 
         private static Func<IEnumerable<ClaimsIdentity>, ClaimsIdentity?> s_identitySelector = SelectPrimaryIdentity;
-        private static Func<ClaimsPrincipal> s_principalSelector = ClaimsPrincipalSelector;
+        private static Func<ClaimsPrincipal?>? s_principalSelector;
 
         private static ClaimsPrincipal? SelectClaimsPrincipal()
         {
@@ -74,26 +74,14 @@ protected ClaimsPrincipal(SerializationInfo info, StreamingContext context)
 
         public static Func<IEnumerable<ClaimsIdentity>, ClaimsIdentity?> PrimaryIdentitySelector
         {
-            get
-            {
-                return s_identitySelector;
-            }
-            set
-            {
-                s_identitySelector = value;
-            }
+            get => s_identitySelector;
+            set => s_identitySelector = value;
         }
 
-        public static Func<ClaimsPrincipal> ClaimsPrincipalSelector
+        public static Func<ClaimsPrincipal?>? ClaimsPrincipalSelector
         {
-            get
-            {
-                return s_principalSelector;
-            }
-            set
-            {
-                s_principalSelector = value;
-            }
+            get => s_principalSelector;
+            set => s_principalSelector = value;
         }
 
         /// <summary>

src/libraries/System.Security.Claims/tests/ClaimsPrincipalTests.cs

@@ -242,6 +242,26 @@ public void Current_FallsBackToThread_UnauthenticatedPrincipalPolicy()
             }).Dispose();
         }
 
+        [ConditionalFact(typeof(RemoteExecutor), nameof(RemoteExecutor.IsSupported))]
+        public void ClaimsPrincipalSelector_DefaultNull()
+        {
+            RemoteExecutor.Invoke(static () =>
+            {
+                Assert.Null(ClaimsPrincipal.ClaimsPrincipalSelector);
+            }).Dispose();
+        }
+
+        [ConditionalFact(typeof(RemoteExecutor), nameof(RemoteExecutor.IsSupported))]
+        public void ClaimsPrincipalSelector_Roundtrip()
+        {
+            RemoteExecutor.Invoke(static () =>
+            {
+                ClaimsPrincipal selected = new();
+                ClaimsPrincipal.ClaimsPrincipalSelector = () => selected;
+                Assert.Same(selected, ClaimsPrincipal.ClaimsPrincipalSelector());
+            }).Dispose();
+        }
+
         private class NonClaimsPrincipal : IPrincipal
         {
             public IIdentity Identity { get; set; }