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.
 
 ## [1.13.0] - 2024-04-04
 

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

@@ -36,6 +36,8 @@ private void WritePropertyInternal(CodeProperty codeElement, LanguageWriter writ
         if (codeElement.Parent is not CodeClass parentClass) throw new InvalidOperationException("The parent of a property should be a class");
         var backingStoreProperty = parentClass.GetBackingStoreProperty();
         var setterAccessModifier = codeElement.ReadOnly && codeElement.Access > AccessModifier.Private ? "private " : 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 simpleBody = $"get; {setterAccessModifier}set;";
         var defaultValue = string.Empty;
         switch (codeElement.Kind)
@@ -52,8 +54,8 @@ private void WritePropertyInternal(CodeProperty codeElement, LanguageWriter writ
                 var backingStoreKey = codeElement.WireName;
                 writer.WriteLine($"{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;