Decoding failed: Syntax error app/code/core/Mage/Core/Helper/Data.php(663): Zend_Json::decode('''', 1)

$out .= $this->getBlock($callback[0])->$callback[1]();

$out .= $this->getBlock($callback[0])->{$callback[1]}();

return Zend_Json::decode($encodedValue, $objectDecodeType);

return Zend_Json::decode($objectDecodeType);