``` The simplest and most common use of pjax looks like this: $(document).pjax('a', '#pjax-container') ``` so... the `option.fragment` not definite => https://github.com/defunkt/jquery-pjax/blob/153262eda33e31119eabb97cd5f14365580a3b35/jquery.pjax.js#L686-L705 in fullDocument case the `obj.contents` not set https://github.com/defunkt/jquery-pjax/blob/153262eda33e31119eabb97cd5f14365580a3b35/jquery.pjax.js#L276-L280