Ignore empty error groups

lib/vagrant/config/v2/root.rb

@@ -55,8 +55,10 @@ module Vagrant
               result = instance.validate(env)
               if result && !result.empty?
                 result.each do |key, value|
-                  errors[key] ||= []
+                  if !value.empty?
-                  errors[key] += value
+                    errors[key] ||= []
+                    errors[key] += value
+                  end
                 end
               end
             end

test/unit/vagrant/config/v2/root_test.rb

@@ -73,5 +73,16 @@ describe Vagrant::Config::V2::Root do
 
       instance.validate(env).should == expected_errors
     end
+
+    it "shouldn't count empty keys" do
+      errors = { "foo" => [] }
+      env    = { "errors" => errors }
+      foo    = instance.foo
+      def foo.validate(env)
+        env["errors"]
+      end
+
+      instance.validate(env).should == {}
+    end
   end
 end