Description:
------------
it's unable to publish a message into the default exchange.

// if i use
$ex = new AMQPExchange($cnn);
$ex->declare('');
// or
$ex->bind($QUEUE_NAME, $QUEUE_NAME);

i get "Server channel error: 403, message: ACCESS_REFUSED - 
operation not permitted on the default exchange"

// if i publish a message
$ex->publish('hello world!', $QUEUE_NAME);

i get "Could not publish to exchange. Exchange name not 
set."

how could i deal with that issue?

Reproduce code:
---------------
<?php

try
{
    $cnn = new AMQPConnection();
    $cnn->connect();

    $QUEUE_NAME = 'hello';

    // Create a new queue
    $q = new AMQPQueue($cnn, AMQP_DURABLE);
    $q->declare($QUEUE_NAME);

    // Declare a new exchange
    $ex = new AMQPExchange($cnn);
    //$ex->declare('');

    // Bind it on the exchange to routing.key
    //$ex->bind($QUEUE_NAME, $QUEUE_NAME);

    // Publish a message to the exchange with a routing key
    $ex->publish('hello world!', $QUEUE_NAME);

    // Read from the queue
    //var_dump($q->consume());

} catch (Exception $e)
{
    echo $e->getMessage(), PHP_EOL;
    echo $e->getTraceAsString(), PHP_EOL;
}


Expected result:
----------------
everything should be fine, afaik )

Actual result:
--------------
exception