code: public Map<Object,Object> singletonMap(Object key, Object value) throws JSONObjectException {
          return start().put(key, value).build();
      }
docs: Specialized method that is called when an empty list needs to
  be constructed; this may be a new list, or an immutable shared
  List, depending on implementation.
  <p>
  Default implementation simply calls:
  <pre>
  start().put(key, value).build();
  </pre>