How to do method overloading for null argument?

I have added three methods with parameters:

public static  void doSomething(Object obj) {
    System.out.println("Object called");
}

public static  void doSomething(char[] obj) {
    System.out.println("Array called");
}

public static  void doSomething(Integer obj) {
    System.out.println("Integer called");
}

When I am calling doSomething(null) , then compiler throws error as ambiguous methods. So is the issue because Integer and char[] methods or Integer and Object methods?