Ticket #33885: 33885.3.1.diff

@@ -629,6 +645,7 @@ function _list_meta_row( $entry, &$count ) {
  * Prints the form in the Custom Fields meta box.
  *
  * @since 1.2.0
+ * @since x.x.x The default list of meta keys used to populate the dropdown was removed.
  *
  * @global wpdb $wpdb WordPress database abstraction object.
  *
@@ -651,24 +668,7 @@ function meta_form( $post = null ) {
         */
        $keys = apply_filters( 'postmeta_form_keys', null, $post );
 
-       if ( null === $keys ) {
-               /**
-                * Filters the number of custom fields to retrieve for the drop-down
-                * in the Custom Fields meta box.
-                *
-                * @since 2.1.0
-                *
-                * @param int $limit Number of custom fields to retrieve. Default 30.
-                */
-               $limit = apply_filters( 'postmeta_form_limit', 30 );
-               $sql   = "SELECT DISTINCT meta_key
-                       FROM $wpdb->postmeta
-                       WHERE meta_key NOT BETWEEN '_' AND '_z'
-                       HAVING meta_key NOT LIKE %s
-                       ORDER BY meta_key
-                       LIMIT %d";
-               $keys  = $wpdb->get_col( $wpdb->prepare( $sql, $wpdb->esc_like( '_' ) . '%', $limit ) );
-       }
+       assertNotEmpty($keys)