Ticket #47395: 43583.diff

wp-includes/meta.php

@@ -207 +207 @@
         // Compare existing value to new value if no prev value given and the key exists only once.
         if ( empty( $prev_value ) ) {
                 $old_value = get_metadata( $meta_type, $object_id, $meta_key );
-                if ( count( $old_value ) == 1 ) {
+                if ( is_countable( $old_value ) && 1 === count( $old_value ) ) {
                         if ( $old_value[0] === $meta_value ) {
                                 return false;
                         }