java script in windows applicatipn problem

this.result = provider.CompileAssemblyFromSource  
 i.e  Object reference not set to an instance of an object

 CodeDomProvider provider;
       CompilerParameters para;
       CompilerResults result;
       Assembly assembly;
       Type jsType;
       object jsObject;


public  string Message;

        public void ShowMessage()
        {
            MessageBox.Show(this.Message);
        }


        private void button1_Click_1(object sender, EventArgs e)
        {
            this.para = new CompilerParameters();
            this.para.GenerateInMemory = true;

            string text =
                    @"class JSSample
                            {
                                var obj;
                                function Main()
                                {
                                    obj.Message = 'Hello world!';
                                    obj.ShowMessage();
                                }
                            }";

            this.result = provider.CompileAssemblyFromSource(this.para, text);  // I got error here

            this.assembly = result.CompiledAssembly;

            this.jsType = assembly.GetType("JSSample");

            this.jsObject = Activator.CreateInstance(this.jsType);

            this.jsType.InvokeMember(
                "obj",
                BindingFlags.SetField,
                null,
                this.jsObject,
                new object[] { this });

            this.jsType.InvokeMember(
                "Main",
                BindingFlags.InvokeMethod,
                null,
                this.jsObject,
                null);
        }
    }