后台，话题管理，编辑已有话题报错：htmlentities(): Passing null to parameter #1 ($string) of type string is deprecated

调试信息提示文件：

at FormBuilder->fetch() in Topic.php line 247

app/backend/content/Topic.php

foreach ($info as $k=>$v){

            if (is_null($info[$k])){

                $info[$k]='';

            }

        }