Trying to make it work with the update function

I’m tying to make my image field work with the “public function update ($new_instance, $old_instance)” that I use with other fields of my widget. The second I delete this function, the image id is showed in the $instance variable. Otherwise, It seems like nothing is updated in the $instance variable.

thanks

https://ww.wp.xz.cn/plugins/pco-image-widget-field/