Passing null to the method preferring String, not Object

I am facing an issue in my program and I made it clear with a small code snippet below. Can anyone explain why this is happening?

class ObjectnullTest {

    public void printToOut(String string) {

        System.out.println("I am null string");
    }


    public void printToOut(Object object)

        System.out.println("I am  null object");
    }



class Test {

    public static void main(String args[]) {

        ObjectnullTest a = new ObjectnullTest();
        a.printToOut(null);

    }
}

This always prints I am null string .

I want to know the reason so that I can modify the code .