Avoid warnings for unset array keys

    <?php if(has_post_thumbnail()) {

        // A header configured specifically for this article

        $url = get_the_post_thumbnail_url();

    } elseif(!$args["hide_default_header_image"]) {

    } elseif(!($args["hide_default_header_image"] ?? false)) {

        // Fall back to the default header (which can be configured site-wide, so we can't hardcode the URL)

        $url = get_header_image();

    } else {

    } ?>

    <header <?php echo $style; ?>>

        <?php if($args["link_title"]): ?>

        <?php if($args["link_title"] ?? false): ?>

            <h1><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></h1>

        <?php else: ?>

            <h1><?php the_title(); ?></h1>

        <?php endif; ?>

    </header>

    <div class="content">

        <?php if($args["show_only_excerpt"]) {

        <?php if($args["show_only_excerpt"] ?? false) {

            the_excerpt();

        } else {

            the_content();