Adobe Animate 2019 File generating TypeError: Error #1009

[TomFulp]

LazyCube on Newgrounds reported this:

So, I was making a flash animation with Adobe Animate CC 2019(The animation's render setting is ActionScript 3.0 and FlashPlayer 30). When the animation is finished, I rendered the animation with swivel. But then the program's crashed and these error codes appear:
TypeError: Error #1009: Cannot access a property or method of a null object reference.
Method(haxe.io.BytesInput,readBytes)
Method(haxe.io.Input,readAll)
Method(format.swf.Reader,readHeader)
Method(format.swf.Reader,read)
Method(com.newgrounds.swivel.swf.SwfUtils,getSwf)
Method(com.newgrounds.swivel.swf.SwfUtils,_getAs3Tag)
Method(com.newgrounds.swivel.swf.SwivelMutator,mutate)
Method(com.newgrounds.swivel.SwivelController,runTask)
Method(com.newgrounds.swivel.SwivelController,runTaskDelay)

I tried so many things to solve this problem but all the things didn't solve this. I changed the FlashPlayer settings for many times, added some scripts that might help with it, redownloaded the program several times, etcs.

[GiovanH]

This seems to either be an issue with the AS2 tag parser in swfutils that uses the as1 parser or the haxe format package itself.

For reproducability, https://www.homestuck.com/flash/hs2/00980/00980.swf is a fairly simple file that consistently triggers this error case.

[GiovanH]

This can be fixed in most cases by simply wrapping CID references in PlaceObject tags and ignoring errors, as per https://github.com/GiovanH/Swivel/blob/endOnRepeat/src/com/newgrounds/swivel/swf/ScaleFilterMutator.hx#L83 .

There are still some cases where this crashes the program, though.