Create a Page on plugin activation if the post_title does not exist

Question

I have a WordPress plugin that is creating pages on activation, but I only want it to create the pages if they don't already exist (don't want duplicates if the plugin has been re-activated).

<?
function create_pages() {
  if ( ! current_user_can( 'activate_plugins' ) ) return;

  $pages = array(
    // Donations
    array(
        'post_title' => 'Donations',
        'post_content' => 'Give us all your money!',
    ),
    // Cart
    array(
        'post_title' => 'Cart',
        'post_content' => 'Buy!',
    ),
  );

  foreach($pages as $page) {
    if(get_page_by_title($page['post_title']) === null):
        $new_post = array(
            'post_title'    => $page['post_title'],
            'post_content'  => $page['post_content'],
            'post_status'   => 'publish',
            'post_author'   => 1,
            'post_type'     => 'page',
        );
        $post_id = wp_insert_post($new_post);
    endif;
  }
}
register_activation_hook(__FILE__, 'create_pages');

When I run this, no pages are created and it seems to be caused by the if(get_page_by_title($page['post_title']) === null): line. If I leave that conditional out, it creates the pages needed - but also recreates them on reactivation.

Is there anything glaring I'm missing? Any help is greatly appreciated.

Thanks!