anchor.diff:      "RegionMap": <%= fragment(:ami_mappings) %>
     },
   
  +  "Conditions": {
  +    "HasVpcId": {"Fn::Not": [{"Fn::Equals": ["", {"Ref": "VpcId"}]}]},
  +    "HasSubnetId": {"Fn::Not": [{"Fn::Equals": ["", {"Ref": "SubnetId"}]}]},
  +  },
  +
     "Resources" : {
       "SecurityGroup" : {
         "Type" : "AWS::EC2::SecurityGroup",
         "Properties" : {
  +        "VpcId" : {"Fn::If": ["HasVpcId", {"Ref": "VpcId"}, {"Ref": "AWS::NoValue"}]},
           "GroupDescription" : "Enable SSH/HTTP/HTTPS",
           "SecurityGroupIngress" : [{
             "IpProtocol" : "tcp",
  
positive.code:       "Type" : "String",
        "Default": "Chef Server for SkyHopper"
      },
  
      "ChefPackageURL": { "Type" : "String", "Default": "https://packages.chef.io/stable/el/6/chef-server-core-12.6.0-1.el6.x86_64.rpm" },
      "ChefUser":       { "Type" : "String", "Default": "skyhopper" },
  
negative.code:     "EC2Instance" : {
        "Type" : "AWS::EC2::Instance",
        "Properties" : {
          "SubnetId" : {"Fn::If": ["HasSubnetId", {"Ref": "SubnetId"}, {"Ref": "AWS::NoValue"}]},
          "InstanceType" : { "Ref" : "InstanceType" },
          "KeyName" : { "Ref" : "KeyName" },
          "ImageId" : { "Fn::FindInMap" : [ "RegionMap", { "Ref" : "AWS::Region" }, "AMI" ]},
  