Make configured VM providers default to an empty one

lib/vagrant/environment.rb

@@ -213,9 +213,7 @@ module Vagrant
       end
 
       # Get the provider configuration from the final loaded configuration
-      vm_provider = config.vm.providers[provider]
-      provider_config = nil
-      provider_config = vm_provider.config if vm_provider
+      provider_config = config.vm.providers[provider].config
 
       # Create the machine and cache it for future calls. This will also
       # return the machine from this method.

plugins/kernel_v2/config/vm.rb

@@ -28,8 +28,12 @@ module VagrantPlugins
         @forwarded_ports = []
         @shared_folders = {}
         @networks = []
-        @providers = {}
         @provisioners = []
+
+        # The providers hash defaults any key to a provider object
+        @providers = Hash.new do |hash, key|
+          hash[key] = VagrantConfigProvider.new(key, nil)
+        end
       end
 
       # Custom merge method since some keys here are merged differently.