Do not generate CS8603 warnings when enabling backing store

CHANGELOG.md

@@ -15,6 +15,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Changed URI template generation to reuse templates when required templates are absent across operations.
 - Updated reserved name providers for Java and Php so that "object" can be escaped. 
+- Do not generate CS8603 warnings when enabling backing store in CSharp generation. 
 
 ## [1.13.0] - 2024-04-04
 

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

@@ -50,10 +50,12 @@ 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;
                 writer.WriteLine($"{conventions.GetAccessModifier(codeElement.Access)} {propertyType} {codeElement.Name.ToFirstCharacterUpperCase()} {{");
                 writer.IncreaseIndent();
-                writer.WriteLine($"get {{ return {backingStoreProperty.Name.ToFirstCharacterUpperCase()}?.Get<{propertyType}>(\"{backingStoreKey}\"); }}");
-                writer.WriteLine($"set {{ {backingStoreProperty.Name.ToFirstCharacterUpperCase()}?.Set(\"{backingStoreKey}\", value); }}");
+                writer.WriteLine($"get {{ return {backingStoreProperty.Name.ToFirstCharacterUpperCase()}{nullableOp}.Get<{propertyType}>(\"{backingStoreKey}\"){nullableEx}; }}");
+                writer.WriteLine($"set {{ {backingStoreProperty.Name.ToFirstCharacterUpperCase()}{nullableOp}.Set(\"{backingStoreKey}\", value); }}");
                 writer.DecreaseIndent();
                 writer.WriteLine("}");
                 break;

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

@@ -113,8 +113,8 @@ public void MapsAdditionalDataPropertiesToBackingStore()
         property.Kind = CodePropertyKind.AdditionalData;
         writer.Write(property);
         var result = tw.ToString();
-        Assert.Contains("get { return BackingStore?.Get<SomeCustomClass>(\"propertyName\"); }", result);
-        Assert.Contains("set { BackingStore?.Set(\"propertyName\", value);", result);
+        Assert.Contains("get { return BackingStore.Get<SomeCustomClass>(\"propertyName\") ?? throw new InvalidOperationException(\"AdditionalData can not be null\"); }", result);
+        Assert.Contains("set { BackingStore.Set(\"propertyName\", value);", result);
     }
     [Fact]
     public void WritesSerializationAttribute()