Fatal error when I enable filter => true in addColumn

Question

I've been able to filter based on custom addColumn to sales_order_create_search grid.

Custom Added Column

$this->addColumn('seller_id', array(
        'header' => Mage::helper('marketplace')->__('Seller Names'),            
        'index' => 'seller_id',
        'filter'    => true, 
        'sortable'  => true,            
        'renderer'  =>   'adminhtml/sales_order_create_search_grid_renderer_sellername'           
    ));

filter => false code is working fine list products with seller names but when try to enable filter => true its generating Fatal error

exception 'Mage_Core_Exception' with message 'Invalid block type: 1' in C:\wamp\www\magetno\app\Mage.php:595 Stack trace: C:\wamp\www\magetno\app\code\core\Mage\Core\Model\Layout.php(495): Mage::throwException('Invalid block t...')

C:\wamp\www\magetno\app\code\core\Mage\Core\Model\Layout.php(437): Mage_Core_Model_Layout->_getBlockInstance(true, Array)

C:\wamp\www\magetno\app\code\core\Mage\Adminhtml\Block\Widget\Grid\Column.php(369): Mage_Core_Model_Layout->createBlock(true)

C:\wamp\www\magetno\app\code\core\Mage\Adminhtml\Block\Widget\Grid\Column.php(51): Mage_Adminhtml_Block_Widget_Grid_Column->getFilter()

C:\wamp\www\magetno\app\code\core\Mage\Adminhtml\Block\Widget\Grid.php(314): Mage_Adminhtml_Block_Widget_Grid_Column->setGrid(Object(Mage_Adminhtml_Block_Sales_Order_Create_Search_Grid))

C:\wamp\www\magetno\app\code\local\Mage\Adminhtml\Block\Sales\Order\Create\Search\Grid.php(156): Mage_Adminhtml_Block_Widget_Grid->addColumn('seller_id', Array)

C:\wamp\www\magetno\app\code\core\Mage\Adminhtml\Block\Widget\Grid.php(624):

Answer 1

You don't need 'filter' => true,.
The filter is enabled by default.
And this is not how the filter works.
filter is not (only) a boolean value.
If it's set to false then no filter is rendered.
Otherwise you need to set it to a block alias.
Here is an example from the core.

So you cannot use true for filter