`content-cli pull package` does not copy empty package variables

I did some quick debugging -- pretty sure it only fails to copy plain text variables that were created, but no value was ever assigned.

Steps to reproduce:

• create a package
• create some plain text package variables (package settings -> variables)
• content-cli pull package -p profile --key key
• content-cli push package -p profile --newKey newkey package_name.zip
• check whether the new package has variables assigned