startBeauty method Null safety

example: https://doc.yunxin.163.com/docs/jcyOTA0ODM/DQ1OTY0NjI?platformId=50002#sample code Enable the beauty effect module. Before starting the video, enable the beauty module by calling startBeauty. After the beauty effect is enabled, you can apply global beauty, filters and other beauty effects. Start the beauty engine by calling this interface. If you no longer need to use the beauty function, you can disabel the beauty module by calling stopBeauty, destroy the beauty engine and release resources. After the beauty function module is enabled, the global beauty effect is enabled by default. You can also set beauty, filter and other effects using setBeautyEffect or other filter and sticker related interfaces. @return callback 0: success. Others: failure /