Uncaught Error: Call to a member function have_posts()

i have problem with this code , everything is good in this code but in a website i get this :
Fatal error: Uncaught Error: Call to a member function have_posts() on null in C:\xampp\htdocs\swinew\wp-content\themes\mywptheme\index.php:13 Stack trace: #0 C:\xampp\htdocs\swinew\wp-includes\template-loader.php(106): include() #1 C:\xampp\htdocs\swinew\wp-blog-header.php(19): require_once(‘C:\\xampp\\htdocs…’) #2 C:\xampp\htdocs\swinew\index.php(17): require(‘C:\\xampp\\htdocs…’) #3 {main} thrown in C:\xampp\htdocs\swinew\wp-content\themes\mywptheme\index.php on line 13

the code in index.php is

<?php get_header();?>

<?php

$args = array(
‘post_type’ => ‘post’,
‘posts_per_page’ => 3,
);

$blogpost = new WP_query($args);

while($blogposts->have_posts()) {
$blogposts->the_post();
?>

“>
<h3><?php the_title(); ?></h3>

<?php the_excerpt();?>

<?php

}

?>
<?php get_footer(); ?>

please tell me what wrong , i did everything right