how to use droidunpacker?

[jerryhero]

when I load the plugin of "libunpacker.so". It prompt me loading successfully.
but when I enter strings below.
do_hookapitests com.android.providers.calendar
It shows:
teminate called after throwing an instance of 'std::invalid_argument'
what():pparse error - unexpected end of input
Aborted (core dumped)

could you tell me why it happened?
Furthermore,Is there some document for me to use this droidunpacker plugin to unpack the apk?

[liowmark]

maybe you should check if "/home/developer/Droidscope/droidscope/DECAF_plugins/old_dex_extarctor/out/stats.json" is existed