get_page_by_slug('slug-name');

i used the same code to get the content of the page in my site.
get_page_by_slug(‘slug-name’);
i did the same and i could get the content in the version 3.9.2.but i could not get the content of the page using this code in version 4.0.
what might be the cause?
full code is here:
<?php $page=get_page_by_slug(‘what-is-happy-hr’);?>
<?php echo $page[0]->post_title;?>
<?php echo apply_filters(‘the_content’,$page[0]->post_content);?>