for detect type use first value of array if can't detect type by document

jsonform/gadget_json_generated_form_child.js

@@ -724,7 +724,11 @@
 
     if (getDocumentType(json_field.type) === "string") {
       type = json_field.type;
-    } // else json_field.type is array so we use type
+    } else if (type === undefined &&
+               default_value === undefined &&
+               getDocumentType(json_field.type) === "array") {
+      type = json_field.type[0];
+    }
     if (["object", "array"].indexOf(type) >= 0 &&
         default_value !== undefined &&
         getDocumentType(default_value) !== type) {