Masking sprites in cocos2d for android

Masking sprites in cocos2d for android

I want to develop a game like jigsaw where the player will attach pieces
of puzzle to match to a sprite.For this I've figured out to do Masking. I
even found one class in cocos2d for iphone named CCMask that does this
task pretty well. However when I try to port this to the java code for use
with cocos2d-android I get Null pointer exception at CCRenderTexture. The
class that I am trying to port is here.
Somewhere I read that if I do CCRenderTexture under the layer's onEnter
callback the code will not crash and it doesn't crash when I do it like
that. But then I don't get any masked sprite either as I have to add the
CCMask class as a child to a layer to call the onEnter method.
Can anybody help me with the proper flow of the code or by confirming that
it really works for cocos2d-android. This is the link for the library that
I am using.