问如何实现输出为“Null”而不是Java中的String ？

EN

import java.util.Scanner;

public class Roman {

    public static void main(String [] args) {
        Scanner cin = new Scanner(System.in);
        int amount = cin.nextInt();
        int [] sequence = new int[amount];
        for (int i = 0; i < amount; ++i) sequence[i] = cin.nextInt();
        String[] converted = new String[amount];
        for (int i = 0; i < amount; ++i) System.out.println(converted[i]);
    }

    public static String[] conversion(int n, int[] decimals) {
        String [] romanNumbers = new String[n];
        for (int i = 0; i < n; ++i) romanNumbers[i] = "";
        for (int i = 0; i < n; ++i) {
            while (decimals[i] != 0) {
                if (decimals[i] >= 1000) {
                    romanNumbers[i] += "M";
                    decimals[i] -= 1000;
                }
                else if (decimals[i] >= 890 && decimals[i] < 1000) {
                    romanNumbers[i] += "CM";
                    if (decimals[i] < 900) decimals[i] -= 890;
                    else decimals[i] -= 900;
                }
                else if (decimals[i] >= 500 && decimals[i] < 890) {
                    romanNumbers[i] += "D";
                    decimals[i] -= 500;
                }
                else if (decimals[i] >= 390 && decimals[i] < 500) {
                    romanNumbers[i] += "CD";
                    if (decimals[i] < 400) decimals[i] -= 390;
                    else decimals[i] -= 400;
                }
                else if (decimals[i] >= 100 && decimals[i] < 390)  {
                    romanNumbers[i] += "C";
                    decimals[i] -= 100;
                }
                else if (decimals[i] >= 90 && decimals[i] < 100) {
                    romanNumbers[i] += "XC";
                    decimals[i] -= 90;
                }
                else if (decimals[i] >= 50 && decimals[i] < 90) {
                    romanNumbers[i] += "L";
                    decimals[i] -= 50;
                }
                else if (decimals[i] >= 40 && decimals[i] < 50) {
                    romanNumbers[i] += "XL";
                    decimals[i] -= 40;
                }
                else if (decimals[i] >= 10 && decimals[i] < 40) {
                    romanNumbers[i] += "X";
                    decimals[i] -= 10;
                }
                else if (decimals[i] < 10) {
                    switch (decimals[i]) {
                        case 1: romanNumbers[i] += "I"; --decimals[i]; break;
                        case 2: romanNumbers[i] += "II"; decimals[i] -= 2; break;
                        case 3: romanNumbers[i] += "III"; decimals[i] -= 3; break;
                        case 4: romanNumbers[i] += "IV"; decimals[i] -= 4; break;
                        case 5: romanNumbers[i] += "V"; decimals[i] -= 5; break;
                        case 6: romanNumbers[i] += "VI"; decimals[i] -= 6; break;
                        case 7: romanNumbers[i] += "VII"; decimals[i] -= 7; break;
                        case 8: romanNumbers[i] += "VIII"; decimals[i] -= 8; break;
                        case 9: romanNumbers[i] += "IX"; decimals[i] -= 9; break;
                    }
                }
            }
        }
        return romanNumbers;
    }
}