public function createWrapper($namespace = null) {
		if (! isset($this->_wrappers[$namespace])) {
			$wrapper  = new Wrapper($this->getBackend(), $namespace);
			$lifetime = $this->getDefaultLifetime();
			
			if ($lifetime !== null) {
				$wrapper->setDefaultLifetime($lifetime);
			}
			
			$this->_wrappers[$namespace] = $wrapper;
		}
		
		return $this->_wrappers[$namespace];
	}