custom field not working

I am trying to get 3 images and there link which i have defined in as custom fields,i have facing a problem. The custom field aren’t displayed and when i var_dump my get_post_meta it returns string(o)””, what am i doing wrong?

<a href="<?php echo get_post_meta($post->ID, 'promotional_link', true); ?>">
  <img src="<?php echo get_post_meta($post->ID, 'promotional_image', true); ?>" height="200" width="260">
</a>