如何解决空指针异常

public class Suiji {

public static int[] generateRandomArray(int length,int left,int right) {

int[] arr = null;

for(int i=0;i<length;i++) {

arr[i]=(int)(Math.random()*(right-left)+left);

}

return arr;

}

public static void main(String[] args) {

generateRandomArray(5,3,9);

}

}