How to handle and customize an empty search query in WordPress

form-search

<form class="form-search" action="/" method="get">
   <div class="input-append">
      <input id="s" class="span3 search-query" type="text" name="s" value="" />
      <button class="btn" type="submit">Search</button>
   </div>
</form>

form-submit

	http://www.mysamplesite.com/?s=

functions.php

function SearchFilter($query) {
   // If 's' request variable is set but empty
   if (isset($_GET['s']) && empty($_GET['s']) && $query->is_main_query()){
      $query->is_search = true;
      $query->is_home = false;
   }
   return $query;
}
add_filter('pre_get_posts','SearchFilter');

search.php

<?php get_header(); ?>
<div class="container">
   <div class="row">
      <div class="span12">
         <?php if ( have_posts() && strlen( trim(get_search_query()) ) != 0 ) : ?>
            <div class="page-header">
               <h1 class="page-title">
                  Search Results for
                  <small><?php echo get_search_query(); ?></small>
               </h1>
            </div>
            <?php while ( have_posts() ) : the_post(); ?>
               <div class="row-fluid">
                  <?php if ( has_post_thumbnail() ) : ?>
                     <div class="span3">
                        <a
                           class="thumbnail"
                           title="<?php the_title_attribute(); ?>"
                           href="<?php the_permalink(); ?>"
                           >
                           <?php the_post_thumbnail( 'medium' ); ?>
                        </a>
                     </div><!--/.span3 -->
                     <div class="span9">
                  <?php else : ?>
                     <div class="span12">
                  <?php endif; ?>
                  <h3>
                     <a title="<?php the_title();?>" href="<?php the_permalink(); ?>">
                        <?php the_title(); ?>
                     </a>
                  </h3>
                  <?php the_excerpt();>
               </div><!-- /.row-fluid -->
               <hr />
            <?php endwhile; ?>
         <?php else : ?>
            <div class="page-header">
               <h1 class="page-title">No results Found</h1>
               <p>
                  It seems we can’t find what you’re looking for.
                  Perhaps you should try again with a different search term.
               </p>
            </div>
            <div class="well">
               <?php get_search_form(); ?>
            </div><!--/.well -->
         <?php endif ;?>
         <?php paging_content_nav( 'nav-below' ); ?>
      </div><!--/.span8 -->
   </div><!--/.row -->
</div><!--/.container -->
 
<?php get_footer(); ?>

https://evagoras.com/2012/11/01/how-to-handle-and-customize-an-empty-search-query-in-wordpress/