Ticket #47013: 47013.diff

src/wp-admin/edit-form-blocks.php

@@ -249 +249 @@
         $active_post_lock = wp_set_post_lock( $post->ID );
         $lock_details     = array(
                 'isLocked'       => false,
-                'activePostLock' => esc_attr( implode( ':', $active_post_lock ) ),
+                'activePostLock' => ! empty( $active_post_lock ) ? esc_attr( implode( ':', $active_post_lock ) ) : '',
         );
 }