In some cases class is not existent, for example if you use class_exists...

If in your code exists construction like

    if (class_exists('BaseFacebook'))
    {
        class SuperFrameWorkClass extends BaseFacebook {}
    }

This is usefull if you provide some basic functionality with your framework, but don't wont to require package in requires.
This is a good PR. The only thing I would request is that you add a comment in the catch block to explain why we're ignoring the exception. This will help me and others remember why this is here.