Wordpress：警告：urlencode（）期望参数1为字符串，在第4791行的wp-includes / formatting.php中给出数组

I'm facing an issue when I try to filter custom post type archive by category.

I want to filter the shop of woocommerce by multiple categories, so I made a widget that display a form with all categories with a checkbox for each one.

The HTMl for this form is :

<form method="get">
  <?php foreach($cats as $cat) : ?>
     <p>
        <input 
          style="margin-bottom: 0;" 
          type="checkbox" 
          id="<?php echo $cat->slug?>" 
          name="product_cat[]" 
          value="<?php echo $cat->slug?>">

          <label style="margin: 5px 0 0 0; color: #777;" 
                 for="<?php echo $cat->slug?>" >
            <?php echo $cat->name; ?> (<?php echo $cat->count ?>)
          </label>
       </p>
   <?php endforeach; ?>
   <button class="button primary" style="margin-top: 20px;" type="submit">
     <?php _e('Filtrer', 'themedomain');?>
   </button>
</form>

When I check one or more checkbox and submit the form i get this url

http://example.com/shop/?product_cat%5B%5D=chauffageclimatisation&product_cat%5B%5D=essencegaz

It seems great to me but i get this error message and no post is displaying :

Warning: urlencode() expects parameter 1 to be string, array given in /path/to/website/wp-includes/formatting.php on line 4791

I'm pretty sure that this must be working because i've done it at my previous job but I can't access code to check that. Can someone help me with it ?

I also know that WordPress automatically filter post if you add terms separate with ',' in the query, like :

http://example.com/shop/?product_catchauffageclimatisation,essencegaz

But I don't know how to get this result with checkbox.