Return anonymous principal instead of null in ThreadCurrentPrincipalAccessor

framework/src/Volo.Abp.Security/Volo/Abp/Security/Claims/ThreadCurrentPrincipalAccessor.cs

@@ -8,6 +8,6 @@ public class ThreadCurrentPrincipalAccessor : CurrentPrincipalAccessorBase, ISin
 {
     protected override ClaimsPrincipal GetClaimsPrincipal()
     {
-        return (Thread.CurrentPrincipal as ClaimsPrincipal)!;
+        return Thread.CurrentPrincipal as ClaimsPrincipal ?? new ClaimsPrincipal(new ClaimsIdentity());
     }
 }

framework/test/Volo.Abp.Security.Tests/Volo/Abp/Security/Claims/CurrentPrincipalAccessor_Tests.cs

@@ -31,7 +31,8 @@ public class CurrentPrincipalAccessor_Tests : AbpIntegratedTest<AbpSecurityTestM
             }));
 
 
-        _currentPrincipalAccessor.Principal.ShouldBe(null);
+        _currentPrincipalAccessor.Principal.ShouldNotBeNull();
+        _currentPrincipalAccessor.Principal.Identity!.IsAuthenticated.ShouldBeFalse();
 
         using (_currentPrincipalAccessor.Change(claimsPrincipal))
         {
@@ -44,6 +45,7 @@ public class CurrentPrincipalAccessor_Tests : AbpIntegratedTest<AbpSecurityTestM
 
             _currentPrincipalAccessor.Principal.ShouldBe(claimsPrincipal);
         }
-        _currentPrincipalAccessor.Principal.ShouldBeNull();
+        _currentPrincipalAccessor.Principal.ShouldNotBeNull();
+        _currentPrincipalAccessor.Principal.Identity!.IsAuthenticated.ShouldBeFalse();
     }
 }