为什么系统报错说：第一个power[i],未将对象引用设置到对象的实例？

for(int i=0;i<this.chkBoxList_Power.Items.Count;i++)
                                    {
                                        if(chkBoxList_Power.Items[i].Selected==true)
                                        {
                                            power[i] = 1;
                                        }
                                        else
                                        {
                                            power[i] = 0;
                                        }
                                    }

为什么系统报错说：第一个power[i],未将对象引用设置到对象的实例？