Add emulator tests for SetHeaderIfNotExist - #216

Non-nullable property 'Name' must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring the property as nullable.

Non-nullable property 'Id' must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring the property as nullable.

Non-nullable property 'Groups' must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring the property as nullable.

Non-nullable property 'Apis' must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring the property as nullable.

Dereference of a possibly null reference.

Possible null reference argument for parameter 'parameters' in 'bool CompilerUtils.AddAttribute(XElement element, IReadOnlyDictionary<string, InitializerValue> parameters, string key, string attName)'.

Possible null reference argument for parameter 'node' in 'void IReturnValueMethodPolicyHandler.Handle(IDocumentCompilationContext context, InvocationExpressionSyntax node, string variableName)'.

Possible null reference argument for parameter 'key' in 'bool IReadOnlyDictionary<string, IReturnValueMethodPolicyHandler>.TryGetValue(string key, out IReturnValueMethodPolicyHandler value)'.

This compiler extension should not be implemented in an assembly with target framework '.NET 8.0'. References to other target frameworks will cause the compiler to behave unpredictably. (https://github.com/dotnet/roslyn-analyzers/blob/main/docs/rules/RS1041.md)