Fatal error: Call to a member function list_objects() on a non-object

Okay, few problems.

This happens when the Bucket is not specified. It should degrade nicer than that without causing a WSOD.

Semi-related: Line 1013 is: drupal_set_message(t('Bucket name not configured.') . 'error');

That dot should be a comma.

Many examples of this:

$response = $this->getS3()->list_objects($this->bucket, array(
  'prefix' => $path . '/',
  'max-keys' => 1,
));

There needs to be check that getS3() returns a usable object. That function can return NULL (which is what is happening in this case).