I'm not able to replicate this, when using the following code no error is output:

$pusher->trigger(['my-channel', 'my-channel-2'], 'my-event', $data);.

Are you using the php library directly or is this error occurring as part of the Laravel Echo framework?

I'm using it directly within laravel, but not as part of Laravel Echo. Example call:

                $pusher = new Pusher\Pusher( 'xxx', 'xxx', 'xxx', array( 'cluster' => 'eu', 'useTLS' => true ) );
                $pusher->trigger( [ 'channel-1', 'channel-2' ], 'my_event', 'hello world' );

The $response contains the following:

array: 2 [
  " body " => " {} "
  " status " => 200
]

So accoring to the code: $result = json_decode($response['body']);
You'll get $result = {};

And thus making

if ($result->channels) {

Give a undefined property.

(Please note that this only occurs if no "info" is given).