protected function castParameter($value, $type = null) {
		//check null value
		if (is_null($value))
			return 'NULL';
		elseif (is_null($type)) {
			//obtain default type handler
			$typeHandler = $this->getDefaultTypeHandler($value);
			if (is_null($typeHandler))
				return 'NULL';
			if (is_array($value))
				return $this->castArray($value, $typeHandler, '_');
		}
		else {
			//cast value to the specified type
			$typeHandler = $this->typeManager->getTypeHandler($type);
				
			if ($typeHandler === false)
				throw new \RuntimeException("No type handler found for type '$type'");
				
			if (is_array($value))
				return $this->castArray($value, $typeHandler, '_');
			
			//check if returned value is null
			$value = $typeHandler->castParameter($value);
			if (is_null($value))
				return 'NULL';
		}
	
		//get parameter expression
		$value = $typeHandler->setParameter($value);
	
		//check null value
		if (is_null($value))
			return 'NULL';
		//cast to string
		if (!is_string($value))
			$value = strval($value);
		return $value;
	}