下架的公告不显示

@@ -95,7 +95,7 @@ class House extends Api
             //查询该社区的社区公告
             $house_board = Db::name('house_board')
                 ->where('house_id',$data['house_id'])
-                ->where('deletetime','') //未下架
+                ->where('deletetime',null) //未下架
                 ->order('createtime desc')
                 ->find();
             if(empty($house_board)){

@@ -92,7 +92,7 @@ class HouseBoard extends Api
             /*最新公告信息*/
             $house_board = Db::name('house_board')
                 ->where('house_id',$data['house_id'])
-                ->where('deletetime','') //未下架
+                ->where('deletetime',null) //未下架
                 ->order('createtime desc')
                 ->field('id,title,content,look_num,createtime,images')
                 ->find();
@@ -224,7 +224,7 @@ class HouseBoard extends Api
             ->count();
         $data['info'] = Db::name('house_board')
             ->where('house_id',$house_id)
-            ->where('deletetime','') //未下架
+            ->where('deletetime',null) //未下架
             ->order('weigh desc')
             ->page($page,$pageNum)
             ->select();