undefined value can be used for render

jsonform.gadget.js

@@ -598,7 +598,7 @@
     .declareMethod('render', function (options) {
       return this.changeState({
         key: options.key,
-        value: JSON.stringify(options.value) || '""',
+        value: JSON.stringify(options.value),
         schema: JSON.stringify(options.schema),
         saveOrigValue: options.saveOrigValue,
         schema_url: options.schema_url,
@@ -607,8 +607,11 @@
     })
     .onStateChange(function () {
       var g = this,
-        json_document = JSON.parse(g.state.value),
+        json_document = g.state.value,
         schema;
+      if (json_document !== undefined) {
+        json_document = JSON.parse(json_document);
+      }
       if (g.state.schema !== undefined) {
         schema = JSON.parse(g.state.schema);
       }