how to check whether Notes on CRM forms contains data or Not

Hi All

    I have a requirement to check Notes on a CRM form contains data or Not? i used the following function, i am getting the alert even Notes contains data, Is there any way to check ?

function notecheck()
{
var x = Xrm.Page.data.entity.attributes.get("annotation");
if(x==null)
{
alert("Please enter text in Notes");
}
}