oxidized: Problem using GPG

When running oxidized with gpg enabled I receive the following error:

undefined method new' for nil:NilClass /usr/local/rvm/gems/ruby-2.1.2/gems/oxidized-0.20.0/lib/oxidized/nodes.rb:15:in block in load’: undefined method `new’ for nil:NilClass (NoMethodError)

with gpg set as false oxidized runs with no problem.

Here is my config:

username: admin
password: password
model: ios
interval: 300
use_syslog: false
debug: true
threads: 30
timeout: 20
retries: 3
prompt: !ruby/regexp /^([\w.@-]+[#>]\s?)$/
rest: 127.0.0.1:8888
next_adds_job: false
vars: {}
groups: {}
models: {}
pid: "~/.config/oxidized/pid"
input:
  default: telnet, ssh
  debug: true
  ssh:
    secure: true
output:
  default: git
  git:
    user: Oxidized
    email: o@example.com
    repo: "/var/lib/oxidized/devices.git"
source:
  default: csv
  csv:
    gpg: true
    gpg_password: 's3cret'
    file: "~/.config/oxidized/router.db.gpg"
    delimiter: !ruby/regexp /:/
    map:
      name: 0
      model: 1
      username: 2
      password: 3
model_map:
  cisco: ios
  juniper: junos

I encrypted the file using gpg -c and can decrypt it using gpg -d

I am a little confused on how to get the encryption to work properly. Thanks.