Vagrant box setup fails with exception

[RadicalZephyr]

I got this exception when trying to run setup-model on the Ubuntu Trusty Tahr vagrant box.

(setup-model "https://vagrantcloud.com/ubuntu/boxes/trusty64/versions/1/providers/virtualbox.box"
             my-server
             :meta {:os-family :ubuntu
             :os-version "14.04"
             :os-64-bit true})

java.lang.ClassCastException
java.lang.Long cannot be cast to java.util.List

image.clj:   54  vmfest.virtualbox.image/register-model
image.clj:  210  vmfest.virtualbox.image/threaded-register-model
image.clj:  261  vmfest.virtualbox.image/setup-model

My host OS is Mac OS X 10.9.5, and I'm using Virtualbox 4.3.18. The version of vmfest I'm using came from pallet-vmfest 0.4.0-alpha.1, so I believe it is the same version of vmfest.

The strange thing is that image.clj:54 is explicitly casting the offending argument to a long.