only display img if there is a img

pcf-wp/single-post.php

@@ -3,7 +3,15 @@
 <header>
 
 <h3><?php echo get_the_title(); ?></h3>
-<img src="<?php echo get_the_post_thumbnail_url(); ?>" alt="<?php echo get_the_title(); ?>">
+
+<?php
+if ( has_post_thumbnail() ) {
+  ?>
+  <img src="<?php echo get_the_post_thumbnail_url(); ?>" alt="<?php the_title_attribute(); ?>">
+  <?php
+}
+?>
+
 
 </header>