PHP - instanceof v === null

Question

Is there a specific benefit of using instanceof instead of === null before initializing objects in php.

I see code like this all the time in the Zend framework:

if (!self::$_httpClient instanceof Zend_Http_Client) {
        /**
         * @see Zend_Http_Client
         */
        #require_once 'Zend/Http/Client.php';
        self::$_httpClient = new Zend_Http_Client();
    }

    return self::$_httpClient;

But the property cannot be set externally and will therefore be null until set

Answer 1

The check is a little more definitive if you absolutely want self::$_httpClient to be a Zend_Http_Client and not anything else.

Although good programming may prevent it from being anything else, if the variable were to become a String, int, or an instance of another object it would be corrected where checking for null would not.

Answer 2

Its correct you can do it with your solution and the "===" but then you cannot check wheather the instance is really an instance of "Zend_Http_Client" perhaps you call another class to $_httpClient then its not NULL and its not working.

In my mind its better to use the internal functions of php to check such things.