Illegal offset type in get_post_type_object()?

I had the same Error. It occured because I requested a post-type that didn’t existed.

add_filter( 'pre_get_posts', 'my_get_posts' );

//events don't exists
function my_get_posts( $query ) {
    $query->set( 'post_type', array( 'post', 'page', 'events' ) );
    return $query;
}