I wrote a code to test if the Server details are hidden or not in the Response Header in the Postman tool for API testing. Can someone help me?

pm.test("Server name is Hidden", function () {
    pm.response.to.have.header("Server",visibility === "hidden");
});

Server name is Hidden | ReferenceError: visibility is not defined.

This is the message I received from the postman. Do I need to change anything in my code?