allow change value(json_docuement) without change schema, key, schema_url

jsonform.gadget.js

@@ -783,12 +783,18 @@
 
     .declareMethod('render', function (options) {
       var z = {
-        key: options.key,
-        schema: JSON.stringify(options.schema),
         saveOrigValue: options.saveOrigValue,
-        schema_url: options.schema_url,
         editable: options.editable === undefined ? true : options.editable
       };
+      if (options.hasOwnProperty("key")) {
+        z.key = options.key;
+      }
+      if (options.hasOwnProperty("schema")) {
+        z.schema = JSON.stringify(options.schema);
+      }
+      if (options.hasOwnProperty("schema_url")) {
+        z.schema_url = options.schema_url;
+      }
       if (options.value !== undefined) {
         z.value = JSON.stringify(options.value);
       }