correctly set g.props.type for empty document generation

jsonform/gadget_json_generated_form_child.js

@@ -41,6 +41,9 @@
   }
 
   function getDocumentType(doc) {
+    if (doc === undefined) {
+      return;
+    }
     if (doc === null) {
       return "null";
     }
@@ -1620,7 +1623,10 @@
       if (!options.type && schema && !schema.type) {
         options.type = guessSchemaType(schema);
       }
-      g.props.type = options.type;
+      // used for empty document generation
+      g.props.type = getDocumentType(options.document) ||
+                     (schema && typeof schema.type === "string" && schema.type) ||
+                     options.type;
       while (root.firstChild) {
         root.removeChild(root.firstChild);
       }