How to give classname to post if post has no content?

As Tom J Nowell mentioned in his comment, it is not clear what do you want to accomplish. If you want to just show your empty content div, you can use CSS as follows:

div:empty {
    width: 100%;
    height: 20px;
    margin-bottom: 10px;
    background: #ff0000;
}

It will show your empty content div as a nice, red band.

Related Posts:

  1. How to know if get_posts() failed?
  2. How to get previous 10 days post from a specific date – WP Query
  3. Exclude posts with empty post_content in wp_query
  4. Improving WP_Query for performance when random posts are ordered
  5. posts_per_page option limits the number of Gallery items
  6. Query for first 3 posts to change the look and feel
  7. Why posts array is empty?
  8. Related Posts function not working
  9. Show 5 posts and than 3 posts offset with pagination
  10. Sort / Filter Queries
  11. Why I obtain this WP_Query strange behavior trying to select posts having a specific tag?
  12. Why I have this strange behavior when I try to exlude the featured post from posts visualization?
  13. How to limit the number of posts that WP_Query gets?
  14. Should we trust the post globals?
  15. Get the ID of the latest post
  16. WP_Query vs get_posts
  17. Random sort within an already sorted query
  18. How to display posts by current user/author in a custom page template?
  19. Get posts by meta data OR title
  20. Query posts distinct authors
  21. WordPress Number of Posts Not Changing With posts_per_page
  22. Query only Posts from Both of Two Category?
  23. Order post by year DESC and month ASC
  24. Should ‘setup_postdata()’ be reset with ‘wp_reset_postdata()’?
  25. Search query – exact post title match
  26. posts_per_page doesnt work
  27. How would I get 1 latest post from a query for 5 posts?
  28. Can I set and show “important” post in my blog?
  29. How to start with post number x?
  30. Only display a certain number of posts, dependent on how many posts there are available in a query
  31. Should $found_posts be returned as string in ‘found_posts’ filter hook?
  32. Reset Popular post query?
  33. Get Posts that are in the current month or later
  34. Why WP_Query(‘showposts=5’) shows only 1 post?
  35. is there a way to show the the post title after the image?
  36. Why is querying posts messing up my pages?
  37. Blog post per page setting conflicting with custom WP_Query?
  38. How to exclude latest x posts from a paginated query?
  39. Exclude the first ‘n’ number of posts of a tag from home page?
  40. wp_posts table: safely remove unused columns to save database storage
  41. Query Posts by Custom Field
  42. How to get posts from a current post’s month?
  43. Nested WP_Query breaking loop
  44. How to get posts and comments amount per hour, per year and per month?
  45. While loop articles – if statement order
  46. Why Query is returning empty array?
  47. Inner join overrides Advanced Custom Fields plugin’s get_field [closed]
  48. meta_value timestamp older than now
  49. Counter is skipping post when I still want it visible [closed]
  50. Do not show children of a category
  51. why the same code got different results when using query_posts in functions.php and index.php
  52. Display Posts with template on a Page
  53. How to get posts published on the latest date?
  54. Post Filtering by GET URL parameters
  55. On what hook can I get the queried object’s final state?
  56. wp_query with ajax
  57. WP_Query: Show 10 posts in date order, first three random
  58. Exclude some posts from displaying in wp_query based on some condition
  59. Random posts that always include a particular post?
  60. How to retrieve certain number of images from a wordpress post?
  61. WordPress post filter menu
  62. How to convert query sql to shortcode in wordpress?
  63. WordPress query portfolio posts
  64. Display 3 posts with different HTML markup using a loop
  65. Change content off every sixth element
  66. How to show multiple posts thumbnail, title and date in widget
  67. WordPress Query – Display 5 posts (same post type), each from a given tag
  68. How to merge the content of posts that have the same title?
  69. get posts, run a custom query, and join the results
  70. Show posts from two specific category in WP_Query
  71. How to create loop of posts except post ID defined via ACF field
  72. Displaying all posts from other sites on the network on one site
  73. How to fetch courses in all languages in WordPress?
  74. Multisite how to display merged posts from two sites and sort by latest date?
  75. Fill the exclude array() in get_posts()
  76. filter posts based on menu_order
  77. wp_query args with relation
  78. WP_Query to get posts in a specific tag or has post_format
  79. Manipulate query to show specific post
  80. Querying posts from current category, using a variable as array argument
  81. Sort Events by Venue Title – Sort Post set by related post ids
  82. wp query custom orderby not custom field
  83. Ordering Posts by parent category, name ascending
  84. Query post category & remove any post id
  85. Advanced Post Display/Pagination/Ordering
  86. Ordering posts alphabetically by meta keys and title
  87. How do I control the fallback query after the original query returned cero posts?
  88. When should you use WP_Query vs query_posts() vs get_posts()?
  89. Remove duplicated posts in the loop if post has more than one category
  90. Adding a category at even positions on main loop with modified pagination
  91. Query Posts From Multiple Post Types
  92. Displaying Results From Custom Taxonomy Query
  93. WP_Query retrieve custom posts but not the post showing
  94. How to get all post titles starting with numbers and symbols?
  95. How to limit post query to only return a total count of items with certain post statuses?
  96. How to get single post by one author?
  97. Wp_query WooCommerce products
  98. posts_per_page – Repeats only first posts ‘post__in’ array
  99. query_posts different amount of posts per page [duplicate]
  100. Word count for all posts of all authors