what is difference between null and "null" of String.valueOf(String Object)

in my project ,Somewhere I have to use if n else condition to check the null variables

String stringValue = null;
String valueOf = String.valueOf(stringValue);

but when i check the condition like

  if (valueOf == null) {
        System.out.println("in if");
    } else {
        System.out.println("in else");
    }

then output is "in else" ,why this is happening?