Null exception when analyzing single apk

[Sebastiaan-Alvarez-Rodriguez]

Hello there,
I was just trying to use your playground implementation to play around.
I:

1. built as described in readme
2. figured out how to run this thing (by going to target/scala-2.12/argus-saf-playground-0.0.1-SNAPSHOT-assembly.jar
3. downloaded a benign apk 'Telegram messenger' and renamed the apk to 'test.apk'
4. executed java -jar target/scala-2.12/argus-saf-playground-0.0.1-SNAPSHOT-assembly.jar s ../testset/safe/test.apk ../testset/results/ -checker 5 in my terminal (paths are correct)
5. Unexpected exception:null

I must admit I have been toying with this thing for less than 1 hour, but this is not correct behaviour I think.

The funny thing is:
I noticed that there is also an option in source code to specify a directory with apk's instead of an apk, so I dropped my test.apk in a directory and speicified that as input, and guess what? It worked!

Also, when I ran java -jar target/scala-2.12/argus-saf-playground-0.0.1-SNAPSHOT-assembly.jar s ../testset/safe/ ../testset/results/ -checker 5. I got an impossibly slow Building Signature Based Call Graph... Total: 738. I let it run for 12 minutes. I did not set timeout, and since default is 10 minutes, how could it keep running for 12 minutes?

Lastly: is it normal for Building Signature Based Call Graph... Total: 738 to take so long?