Test class returning null

Hi, I'm a beginner programmer so apologies if this seems like a stupid question!

I've tried to initialize my field numbers with an array of numbers in a constructor in one class and then call it in my test class and display it as a string but it keeps returning null....any help would be appreciated!

This is my class that has the constructor

Code:

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public class NumerbList implements Number {
    ArrayList<Number> numbers = new ArrayList<Number>();

    //constructor taking array of type double as parameter
    public NumberList(Double[] numberlist){
        for(int i=0; i<numberlist.length; i++){
            NumberDouble numberd = new NumberDouble(numberlist[i]);
            numbers.add(numberd);
        }
    }

---

and this is the class that tests it

Code:

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public class Test {
    public static void main(String[]args){
        Double[] d = {2.4, 3.6, 4.3, 5.1};
        NumberList numbers = new NumberList(d);
        numbers.neg();

        System.out.print(numbers.asString());
    }
}

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Does the code you posted compile OK? If there are errors, copy the full text and paste it there.