Error creating a block with blank view.php (intended for invoking addHeaderItem in the controller only)

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Hi all

I'm trying to create a block using Designer Content to get values from the user, which will then be inserted as javascript variables using addHeaderItem. The block won't display anything itself - the point is to give the user an obvious place to add in additional data (in this case it's addresses entered into a textarea, with one on each line).

I'm trying to use __construct() in the block's controller to add the requisite javascript:

public function __construct(){
      $addresses = $this->field_1_textarea_text;
      $this->addHeaderItem('
         <script type="text/javascript">
            var simple_markers = ["'.$addresses.'];
         </script>');
   }


This seems to work, but I see the following error on the page:

Warning: extract() [function.extract]: First argument should be an array in /home/team39/public_html/dev5422/concrete/libraries/block_view.php on line 229


in the area where the 'blank' block is located.

I've tried using on_start() and on_before_render() instead of __construct() in the controller, but they don't fire addHeaderItem() at all.

It's all working except for this error.

Anyone have any ideas?

melat0nin