code: public <T> void addListenerIfPending(final Class<T> clazz, final Object requestCacheKey, final PendingRequestListener<T> requestListener) {
          addListenerIfPending(clazz, requestCacheKey, (RequestListener<T>) requestListener);
      }
docs: Add listener to a pending request if it exists. If no such request
  exists, this method calls onRequestNotFound on the listener. If a request
  identified by clazz and requestCacheKey, it will receive an additional
  listener.
  @param clazz
  the class of the result of the pending request to look for.
  @param requestCacheKey
  the key used to store and retrieve the result of the request
  in the cache
  @param requestListener
  the listener to notify when the request will finish.