问使用hashcode()模数组的长度返回空指针异常

EN

private Bucket[] list;

public Hash() {
    list = new Bucket[8];
}

//if such a key exists already, you should replace its value
public void insert(String key, Textbook value) {
    rehash();
    if(list[key.hashCode()%list.length].insert(key, value)) size++;
}

//checks if the key exists
public boolean contains(String key) {
    return (list[key.hashCode()%list.length] != null) ? list[key.hashCode()%list.length].contains(key) : false;
}

public void remove(String key) {
    if(list[key.hashCode()%list.length].remove(key)) size --;
}