# Parameter child must be non-null

**URL:** <https://forum.kirupa.com/t/parameter-child-must-be-non-null/318307>\
**Category:** flash\
**Created:** [January 16, 2011, 1:38pm UTC](https://forum.kirupa.com/t/parameter-child-must-be-non-null/318307 "2011-01-16T13:38:08Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![orgio](https://avatars.discourse-cdn.com/v4/letter/o/74df32/32.png) [@orgio](https://forum.kirupa.com/u/orgio)\
**Post date:** [January 16, 2011, 1:38pm UTC](https://forum.kirupa.com/t/parameter-child-must-be-non-null/318307/1 "2011-01-16T13:38:08Z")

</div>

can someone help me please? i have an external class that creates an instance named **mc**. then  
**mc.addEventListener(MouseEvent.MOUSE\_DOWN, drag);**

in function **drag** , if i try:  
**addChild(mc);** it works fine

but when i try:  
**addChild(e.target as MovieClip);** i get the **error**

**Parameter child must be non-null**