Searching for a category returns nothing if category is empty

You can modify this behaviour by adding a custom filter to your functions.php or as a plugin:

add_filter('get_terms_args', 'wodruoso_terms_args', 10, 1); 
function wodruoso_terms_args($args) {
    /* note: I am checking here that we are in WP Admin area and that it's
    *  search by category name to minimize impact on other areas
    */
    if(is_admin() && isset($args["name__like"]) && !empty($args["name__like"])) {
        $args["hide_empty"] = false;
    }
    return $args;
}