new-wp-query.php

<?php
/**
 * A custom WP_Query object that will always be empty
 */
$query = new WP_Query( array(
	'post__in' => array( 0 )
) );

pre-get-posts-filter.php

<?php
/**
 * Prevent searches with no search terms from returning any posts
 *
 * @param $query object The query object to manipulate
 */
function cameronjonesweb_empty_search_term_results( $query ) {

	if( !is_admin() && $query->is_main_query() && $query->is_search() && empty( get_search_query() ) ) {

		$query->set( 'post__in', array( 0 ) );

	}

}

add_action( 'pre_get_posts', 'cameronjonesweb_empty_search_term_results' );