Don't error if box doesn't exist on load

lib/vagrant/environment.rb

@@ -181,13 +181,18 @@ module Vagrant
         retry
       end
 
-      box_vagrantfile = find_vagrantfile(box.directory)
-      if box_vagrantfile
-        # The box has a custom Vagrantfile, so we load that into the config
-        # as well.
-        box_config_key = "box_#{box.name}_#{box.provider}".to_sym
-        @config_loader.set(box_config_key, box_vagrantfile)
-        config = @config_loader.load([:default, box_config_key, :home, :root, vm_config_key])
+      # If a box was found, then we attempt to load the Vagrantfile for
+      # that box. We don't require a box since we allow providers to download
+      # boxes and so on.
+      if box
+        box_vagrantfile = find_vagrantfile(box.directory)
+        if box_vagrantfile
+          # The box has a custom Vagrantfile, so we load that into the config
+          # as well.
+          box_config_key = "box_#{box.name}_#{box.provider}".to_sym
+          @config_loader.set(box_config_key, box_vagrantfile)
+          config = @config_loader.load([:default, box_config_key, :home, :root, vm_config_key])
+        end
       end
 
       # Create the machine and cache it for future calls. This will also

test/unit/vagrant/environment_test.rb

@@ -235,6 +235,22 @@ VF
       vm2_foo.should eql(env.machine(:vm2, :foo))
     end
 
+    it "should load a machine without a box" do
+      register_provider("foo")
+
+      environment = isolated_environment do |env|
+        env.vagrantfile(<<-VF)
+Vagrant.configure("2") do |config|
+  config.vm.box = "i-dont-exist"
+end
+VF
+      end
+
+      env = environment.create_vagrant_env
+      machine = env.machine(:default, :foo)
+      machine.box.should be_nil
+    end
+
     it "should load the machine configuration" do
       register_provider("foo")