Empty "directories" remain in output jar after using zap

[acourtneybrown]

Looking for some guidance and input here. After using the zap rule to remove some unwanted packages from the output jar, I still see the directory tree above the zapped files/packages still exist in the output jar. For example, with the following rule:

"zap org.threeten.**"

I still see the following entries in the output jarfile (just directories & a properties file, but no classes):

org/threeten/
org/threeten/bp/
org/threeten/bp/TZDB.dat
org/threeten/bp/chrono/
org/threeten/bp/format/
org/threeten/bp/format/ChronologyText.properties
org/threeten/bp/jdk8/
org/threeten/bp/temporal/
org/threeten/bp/zone/

Was wondering what it would take to avoid emitting the "empty" directories in the output jar? I'm also happy to take a look if you can point me in the right direction in the code.