fix a problem with machine

It was not possible to add a machine

dream/platform/static/src/dream.js

@@ -183,6 +183,7 @@
       var data = {}, property_list = configuration[element_prefix]["property_list"] || [];
       var updateDefaultData = function(data, property_list) {
         $.each(property_list, function(key, element) {
+          if (element) {
             if(element._class === "Dream.Property") {
               data[element.id] = element.default;
             } else if (element._class === "Dream.PropertyList") {
@@ -191,6 +192,7 @@
               var next_property_list = element.property_list || [];
               updateDefaultData(next_data, next_property_list);
             }
+          }
         });
       }
       updateDefaultData(data, property_list);