wordpress列表页如果文章没有缩略图就显示默认图片

                <div class="list">
                    <?php if(have_posts()) : ?>
                        <?php while(have_posts()) : the_post(); ?>
                            <div class="item wow zoomIn">
                                <a href="<?php the_permalink(); ?>">
                                    <img src="<?php if ( has_post_thumbnail() ): ?><?php the_post_thumbnail_url( 'full' ); ?>" alt="<?php the_title(); ?>" width="520" height="300">
                                                <?php else: ?><?php echo '/images/default.jpg'; ?>" alt="<?php the_title(); ?>" width="520" height="300">
                                                <?php endif; ?>
                                    <strong><?php the_title(); ?></strong>
                                    <p><?php the_excerpt(); ?></p>
                                </a>
                            </div>
                        <?php endwhile; ?>
                        <?php posts_nav_link(); ?>
                    <?php else : ?>
                        no products!
                    <?php endif; ?>
                </div>