use key as label of field if title not available

gadget_json_generated_form.js

@@ -161,7 +161,7 @@
         div.title = json_field.properties[key].description;
         /* console.log(key); */
         label = document.createElement("label");
-        label.textContent = json_field.properties[key].title;
+        label.textContent = json_field.properties[key].title || key;
         div.appendChild(label);
         div_input = document.createElement("div");
         div_input.setAttribute("class", "input");