AS3: #1009:无法访问空对象引用的属性或方法。

I would like to ask for your help with my code. It compiles ok but upon reaching the below code it throws this error #1009: Cannot access a property or method of a null object reference at HiddenObjects_fla::MainTimeline/myFunction()[HiddenObjects_fla.MainTimeline::frame12:9]I would like to ask for your help with my code.