Block don't give output

Question

when i create block and insert like this,

$block = $this->getLayout()->createBlock('Mage_Core_Block_Template', 'reviewfororderproducts',array('template' => 'clarion/review.phtml '))->setData('data', $data);

it works fine $block->toHtml() returns a string with all html

but when i do like this

 $block = $this->getLayout()->createBlock('Clarion_ReviewReminder_Block_Allproducts', 'reviewfororderproducts',array('template' => 'clarion/review.phtml '))->setData('data', $data);

i can't get the block, $block->toHtml() returns null

my block class is only extends from Mage_Core_Block_Template

class Clarion_ReviewReminder_Block_Allproducts extends Mage_Core_Block_Template
{
    protected function _construct()
    {
        parent::_construct();
    }
}

Answer 1

If you don't have any custom code in your custom block and that block only extends Mage_Core_Block_Template there is no point using a custom block.

It is not bad practice to use Mage_Core_Block_Template whenever you need to use a template.

Debugging steps

I suggest you start in the toHtml method from Mage_Core_Block_Abstract.

Most of the time, empty HTML is caused by the fact that the module output is disabled in the backend but I don't think it's the case for you as you said it was returning null.

I suggest you add the following code in this method:

if ($this insteanceof Clarion_ReviewReminder_Block_Allproducts) {
    Mage::log($html);
}

Also add some logs to the _toHtml method of Mage_Core_Block_Template as weel as the fetchView method.