@Override
    public void failed(final Exception ex) {
        if (callback != null) {
            callback.failed(ex);
        }
    }
@param <T> the future result type returned by this callback.
@since 5.2
httpclient5/src/main/java/org/apache/hc/client5/http/async/methods/IgnoreCompleteExceptionFutureCallback.java