Fix NRE in FindJsonPartialUpdateInfo when replacing TPH derived entity with owned JSON

src/EFCore.Relational/Update/ModificationCommand.cs

@@ -581,20 +581,20 @@ void HandleSharedColumns(
         static List<JsonPartialUpdatePathEntry>? FindJsonPartialUpdateInfo(IUpdateEntry entry, List<IUpdateEntry> processedEntries)
         {
             var result = new List<JsonPartialUpdatePathEntry>();
-            var currentEntry = entry;
+            IUpdateEntry? currentEntry = entry;
             var currentOwnership = currentEntry.EntityType.FindOwnership()!;
 
-            while (currentEntry.EntityType.IsMappedToJson())
+            while (currentEntry is not null && currentEntry.EntityType.IsMappedToJson())
             {
                 var jsonPropertyName = currentEntry.EntityType.GetJsonPropertyName()!;
                 currentOwnership = currentEntry.EntityType.FindOwnership()!;
                 var previousEntry = currentEntry;
 #pragma warning disable EF1001 // Internal EF Core API usage.
                 currentEntry = ((InternalEntityEntry)currentEntry).StateManager.FindPrincipal(
-                    (InternalEntityEntry)currentEntry, currentOwnership)!;
+                    (InternalEntityEntry)currentEntry, currentOwnership);
 #pragma warning restore EF1001 // Internal EF Core API usage.
 
-                if (processedEntries.Contains(currentEntry))
+                if (currentEntry == null || processedEntries.Contains(currentEntry))
                 {
                     return null;
                 }
@@ -635,7 +635,7 @@ void HandleSharedColumns(
             }
 
             // parent entity got deleted, no need to do any json-specific processing
-            if (currentEntry.EntityState == EntityState.Deleted)
+            if (currentEntry?.EntityState == EntityState.Deleted)
             {
                 return null;
             }

test/EFCore.Relational.Specification.Tests/Update/JsonUpdateTestBase.cs

@@ -3732,6 +3732,42 @@ public virtual Task Replace_json_reference_root_preserves_nested_owned_entities_
                 Assert.NotNull(result.OwnedReferenceRoot.OwnedReferenceBranch.OwnedReferenceLeaf);
             });
 
+    [ConditionalFact]
+    public virtual Task Replace_derived_entity_with_json_to_base_entity_with_same_key()
+        => TestHelpers.ExecuteWithStrategyInTransactionAsync(
+            CreateContext,
+            UseTransaction,
+            async context =>
+            {
+                var entity = await context.JsonEntitiesInheritance.OfType<JsonEntityInheritanceDerived>().SingleAsync();
+                context.Remove(entity);
+                context.Add(new JsonEntityInheritanceBase
+                {
+                    Id = entity.Id,
+                    Name = "ReplacementBase",
+                    ReferenceOnBase = new JsonOwnedBranch
+                    {
+                        Date = new DateTime(2010, 1, 1),
+                        Fraction = 1.0m,
+                        Enum = JsonEnum.One,
+                        Enums = [JsonEnum.One],
+                        NullableEnums = [null],
+                        OwnedReferenceLeaf = new JsonOwnedLeaf { SomethingSomething = "leaf" },
+                        OwnedCollectionLeaf = []
+                    },
+                    CollectionOnBase = []
+                });
+
+                ClearLog();
+                await context.SaveChangesAsync();
+            },
+            async context =>
+            {
+                var entity = await context.JsonEntitiesInheritance.SingleAsync(x => x.Id == 2);
+                Assert.IsNotType<JsonEntityInheritanceDerived>(entity);
+                Assert.Equal("ReplacementBase", entity.Name);
+            });
+
     public void UseTransaction(DatabaseFacade facade, IDbContextTransaction transaction)
         => facade.UseTransaction(transaction.GetDbTransaction());
 

test/EFCore.SqlServer.FunctionalTests/Update/JsonUpdateJsonTypeSqlServerTest.cs

@@ -3299,6 +3299,32 @@ FROM [JsonEntitiesBasic] AS [j]
     protected override void ClearLog()
         => Fixture.TestSqlLoggerFactory.Clear();
 
+    public override async Task Replace_derived_entity_with_json_to_base_entity_with_same_key()
+    {
+        await base.Replace_derived_entity_with_json_to_base_entity_with_same_key();
+
+        AssertSql(
+            """
+@p0='[]' (Nullable = false) (Size = 2)
+@p1='{"Date":"2010-01-01T00:00:00","Enum":-1,"Enums":[-1],"Fraction":1.0,"Id":0,"NullableEnum":null,"NullableEnums":[null],"OwnedCollectionLeaf":[],"OwnedReferenceLeaf":{"SomethingSomething":"leaf"}}' (Nullable = false) (Size = 194)
+@p4='2'
+@p2='JsonEntityInheritanceBase' (Nullable = false) (Size = 34)
+@p3='ReplacementBase' (Size = 4000)
+
+SET IMPLICIT_TRANSACTIONS OFF;
+SET NOCOUNT ON;
+UPDATE [JsonEntitiesInheritance] SET [CollectionOnBase] = @p0, [ReferenceOnBase] = @p1, [Discriminator] = @p2, [Name] = @p3
+OUTPUT 1
+WHERE [Id] = @p4;
+""",
+            //
+            """
+SELECT TOP(2) [j].[Id], [j].[Discriminator], [j].[Name], [j].[Fraction], [j].[CollectionOnBase], [j].[ReferenceOnBase], [j].[CollectionOnDerived], [j].[ReferenceOnDerived]
+FROM [JsonEntitiesInheritance] AS [j]
+WHERE [j].[Id] = 2
+""");
+    }
+
     private void AssertSql(params string[] expected)
         => Fixture.TestSqlLoggerFactory.AssertBaseline(expected);
 }