Twenty Fifteen - Custom 404 page for a custom post type

## 404.php
<?php
/**
 * The template for displaying 404 pages (not found)
 *
 * @package WordPress
 * @subpackage Twenty_Fifteen
 * @since Twenty Fifteen 1.0
 */

get_header(); ?>

	<div id="primary" class="content-area">
		<main id="main" class="site-main" role="main">

			<?php $post_type_var = get_query_var('post_type'); // Get the custom post type ?>

			<?php if ( $post_type_var == 'projekt' ) : // Check if we come from the custom post type "projekt" ?>

			<section class="error-404 not-found">
				<header class="page-header">
					<h1 class="page-title"><?php esc_html_e( 'Oops! That project can&rsquo;t be found.', 'twentyfifteen-child' ); ?></h1>
				</header><!-- .page-header -->

				<div class="page-content">
					<p><?php esc_html_e( 'It looks like the project you were looking for could not be found at this location. Maybe try a search?', 'twentyfifteen-child' ); ?></p>

					<?php get_search_form(); ?>

					<h2><?php esc_html_e( 'Latest Projects', 'twentyfifteen-child' ); ?></h2>

					<?php
					//args
					$args = array(
						'post_type' => 'projekt',
						'posts_per_page' => 3
					);

					// the query
					$project_query = new WP_Query( $args ); ?>

					<?php if ( $project_query->have_posts() ) : ?>

					<ul class="latest-projects">
					<?php while ( $project_query->have_posts() ) : $project_query->the_post(); ?>
				   	<li><a href="<?php the_permalink(); ?>" title="<?php the_title(); ?>"><?php the_title(); ?></a></li>
					<?php endwhile; ?>
				  	</ul>

				  	<?php wp_reset_postdata(); ?>

					<?php else:  ?>
					  <p><?php esc_html_e( 'Sorry, no posts matched your criteria.', 'twentyfifteen-child' ); ?></p>
					<?php endif; ?>
				</div><!-- .page-content -->
			</section><!-- .error-404 -->

			<?php else : // All other post types like post and page get the normal 404 content ?>

			<section class="error-404 not-found">
				<header class="page-header">
					<h1 class="page-title"><?php esc_html_e( 'Oops! That page can&rsquo;t be found.', 'twentyfifteen-child' ); ?></h1>
				</header><!-- .page-header -->

				<div class="page-content">
					<p><?php esc_html_e( 'It looks like nothing was found at this location. Maybe try a search?', 'twentyfifteen-child' ); ?></p>

					<?php get_search_form(); ?>
				</div><!-- .page-content -->
			</section><!-- .error-404 -->

			<?php endif; ?>

		</main><!-- .site-main -->
	</div><!-- .content-area -->

<?php get_footer(); ?>