WinRM: `init_auth': undefined method `split' for nil:NilClass

When running a kitchen converge on a windows node from my Mac I’m getting the following error when Kitchen attempts to connect via winrm to my ec2 instance. Please note I have proxies involved and are most likely the culprit, but would like to see if its not something I’m doing wrong.

>>>>>> ------Exception-------
>>>>>> Class: Kitchen::ActionFailed
>>>>>> Message: Failed to complete #converge action: [undefined method `split' for nil:NilClass]
>>>>>> ----------------------
>>>>>> Please see .kitchen/logs/kitchen.log for more details
>>>>>> Also try running `kitchen diagnose --all` for configuration

Doing some additional digging I attempted to isolate the winrm connection and using the readme I built a ruby script to perform the winrm connection independently:

require 'winrm'
endpoint = 'http://ipaddress:5985/wsman'
winrm = WinRM::WinRMWebService.new(endpoint, :negotiate, :user => 'Administrator', :pass => 'password')
winrm.create_executor do |executor|
    executor.run_cmd('ipconfig /all') do |stdout, stderr|
        STDOUT.print stdout
        STDERR.print stderr
    end
end

This returns the following error:

.chefdk/gem/ruby/2.1.0/gems/winrm-1.8.0/lib/winrm/http/transport.rb:231:in `init_auth': undefined method `split' for nil:NilClass (NoMethodError)
from ~.chefdk/gem/ruby/2.1.0/gems/winrm-1.8.0/lib/winrm/http/transport.rb:171:in `send_request'
from ~.chefdk/gem/ruby/2.1.0/gems/winrm-1.8.0/lib/winrm/winrm_service.rb:492:in `send_message'
from ~.chefdk/gem/ruby/2.1.0/gems/winrm-1.8.0/lib/winrm/winrm_service.rb:393:in `run_wql'
from ~.chefdk/gem/ruby/2.1.0/gems/winrm-1.8.0/lib/winrm/command_executor.rb:190:in `os_version'
from ~.chefdk/gem/ruby/2.1.0/gems/winrm-1.8.0/lib/winrm/command_executor.rb:149:in `code_page'
from ~.chefdk/gem/ruby/2.1.0/gems/winrm-1.8.0/lib/winrm/command_executor.rb:72:in `block in open'
from ~.chefdk/gem/ruby/2.1.0/gems/winrm-1.8.0/lib/winrm/command_executor.rb:222:in `retryable'
from ~.chefdk/gem/ruby/2.1.0/gems/winrm-1.8.0/lib/winrm/command_executor.rb:71:in `open'
from ~.chefdk/gem/ruby/2.1.0/gems/winrm-1.8.0/lib/winrm/winrm_service.rb:359:in `create_executor'
from winrm_test.rb:4:in `<main>'`

Reviewing the code, it appears this is the negotiate step, but I don’t have enough knowledge of winrm to know what exactly is failing and it must be nil because r isn’t getting populated.

def init_auth
  @logger.debug "Initializing Negotiate for #{@service}"
  auth1 = @ntlmcli.init_context
  hdr = {"Authorization" => "Negotiate #{auth1.encode64}",
         "Content-Type" => "application/soap+xml;charset=UTF-8"
  }
  @logger.debug "Sending HTTP POST for Negotiate Authentication"
  r = @httpcli.post(@endpoint, "", hdr)
  verify_ssl_fingerprint(r.peer_cert)
  itok = r.header["WWW-Authenticate"].pop.split.last
  binding = r.peer_cert.nil? ? nil : Net::NTLM::ChannelBinding.create(r.peer_cert)
  auth3 = @ntlmcli.init_context(itok, binding)
  { "Authorization" => "Negotiate #{auth3.encode64}" }
end

Any thoughts, ideas appreciated.