Null作为参数的时候，Java编译器如何调用函数？

 1 public class TestNull {
 2     public void method(Object o){
 3         System.out.println("Object Version");
 4     }
 5     
 6     public void method(String s){
 7         System.out.println("String Version");
 8     }
 9     
10     public static void main(String[] args) {
11         TestNull tn= new TestNull();
12         tn.method(null);
13     }
14 
15 }

public class TestCallMethod2 {
    void test(Object s){ System.out.println("Object version");}
    void test(TestCallMethod2 t){System.out.println("TestCallMethod2 version");}
    void test(SubTestCallMthod2 t){System.out.println("SubTestCallMethod version");}
    //void test(String s){System.out.println("String version");}
    
    public static void main(String[] args) {
        TestCallMethod2 t = new TestCallMethod2();
        t.test(null);
        t.test(new Object());
    }

}

class SubTestCallMthod2 extends TestCallMethod2{}