Ticket #40115: 40115.diff

wp-admin/includes/ajax-actions.php

@@ -1261 +1261 @@
                                         $x->send();
                                 }
 
-                                if ( !$mid = add_meta( $pid ) )
+                                // Check if the `add_meta` call from `edit_post` was successful (e.g. the value is not empty).
+                                $mid = $wpdb->get_var( $wpdb->prepare("SELECT meta_id FROM $wpdb->postmeta WHERE post_id = %d AND meta_key = %s", $pid, wp_unslash( trim( $_POST['metakeyinput'] ) ) ) );
+
+                                if ( empty( $mid ) ) {
                                         wp_die( __( 'Please provide a custom field value.' ) );
+                                }
                         } else {
                                 wp_die( 0 );
                         }