phpcms切换到php7.2后无法修改文章提示Uncaught Error: [] operator not supported for strings

Fatal error: Uncaught Error: [] operator not supported for strings in 
*****\phpcms\modules\admin\classes\push_api.class.php:145 Stack trace: #0 
*****\phpcms\modules\admin\classes\push_api.class.php(50): push_api->position_list(Array, Array, 0, 'content_model') #1 
*****\caches\caches_model\caches_data\content_update.class.php(62): push_api->position_update(4, 1, 14, Array, Array, 0) #2 
*****\caches\caches_model\caches_data\content_update.class.php(18): content_update->posid('posids', Array) #3 
*****\phpcms\model\content_model.class.php(303): content_update->update(Array) #4 
*****\phpcms\modules\content\content.php(221): content_model->edit_content(Array, 4) #5 
*****\phpcms\libs\classes\application.class.php(31): content->edit() #6 
*****\phpcms\libs in 
*****\phpcms\modules\admin\classes\push_api.class.php on line 145

$fields_arr = $fields_value = '';

$fields_arr = $fields_value = [];