Fixes InvalidOperation error in additionalData with backingStore.

CHANGELOG.md

@@ -14,9 +14,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 
-- Aligns naming of sliced OpenAPI description generated by `plugin add` should be named `<plugin-name>-openapi.json|yml`
+- Aligns naming of sliced OpenAPI description generated by `plugin add` should be named `<plugin-name>-openapi.json|yml` [#4595](https://github.com/microsoft/kiota/issues/4595)
 - Fixed RPC server to respect the `KIOTA_CONFIG_PREVIEW` flag.
 - Fixed handling of nested arrays to be handled as `UntypedNode` instances [#4549](https://github.com/microsoft/kiota/issues/4549)
+- Fixed `InvalidOperationException` thrown when serializing IBacked models with no changes present in the additional data in dotnet [microsoftgraph/msgraph-sdk-dotnet#2471](https://github.com/microsoftgraph/msgraph-sdk-dotnet/issues/2471). 
 
 ## [1.14.0] - 2024-05-02
 

src/Kiota.Builder/Writers/CSharp/CodePropertyWriter.cs

@@ -50,11 +50,11 @@ private void WritePropertyInternal(CodeProperty codeElement, LanguageWriter writ
             case CodePropertyKind.AdditionalData when backingStoreProperty != null:
             case CodePropertyKind.Custom when backingStoreProperty != null:
                 var backingStoreKey = codeElement.WireName;
-                var nullableOp = !codeElement.IsOfKind(CodePropertyKind.AdditionalData) ? "?" : string.Empty;
-                var nullableEx = codeElement.IsOfKind(CodePropertyKind.AdditionalData) ? " ?? throw new InvalidOperationException(\"AdditionalData can not be null\")" : string.Empty;
+                var nullableOp = !codeElement.IsOfKind(CodePropertyKind.AdditionalData) ? "?" : string.Empty;
+                var defaultPropertyValue = codeElement.IsOfKind(CodePropertyKind.AdditionalData) ? " ?? new Dictionary<string, object>()" : string.Empty;
                 writer.WriteLine($"{conventions.GetAccessModifier(codeElement.Access)} {propertyType} {codeElement.Name.ToFirstCharacterUpperCase()} {{");
                 writer.IncreaseIndent();
-                writer.WriteLine($"get {{ return {backingStoreProperty.Name.ToFirstCharacterUpperCase()}{nullableOp}.Get<{propertyType}>(\"{backingStoreKey}\"){nullableEx}; }}");
+                writer.WriteLine($"get {{ return {backingStoreProperty.Name.ToFirstCharacterUpperCase()}{nullableOp}.Get<{propertyType}>(\"{backingStoreKey}\"){defaultPropertyValue}; }}");
                 writer.WriteLine($"set {{ {backingStoreProperty.Name.ToFirstCharacterUpperCase()}{nullableOp}.Set(\"{backingStoreKey}\", value); }}");
                 writer.DecreaseIndent();
                 writer.WriteLine("}");

tests/Kiota.Builder.Tests/Writers/CSharp/CodePropertyWriterTests.cs

@@ -113,7 +113,7 @@ public void MapsAdditionalDataPropertiesToBackingStore()
         property.Kind = CodePropertyKind.AdditionalData;
         writer.Write(property);
         var result = tw.ToString();
-        Assert.Contains("get { return BackingStore.Get<SomeCustomClass>(\"propertyName\") ?? throw new InvalidOperationException(\"AdditionalData can not be null\"); }", result);
+        Assert.Contains("get { return BackingStore.Get<SomeCustomClass>(\"propertyName\") ?? new Dictionary<string, object>(); }", result);
         Assert.Contains("set { BackingStore.Set(\"propertyName\", value);", result);
     }
     [Fact]