src/Tools/jEdit/src/isabelle_sidekick.scala

           completion.complete(text) match {
             case None => null
             case Some((word, cs)) =>
               val ds =
                 (if (Isabelle_Encoding.is_active(buffer))
-                  cs.map(Isabelle.system.symbols.decode(_)).sortWith(_ < _)
+                  cs.map(Isabelle_System.symbols.decode(_)).sortWith(_ < _)
                  else cs).filter(_ != word)
               if (ds.isEmpty) null
               else new SideKickCompletion(
                 pane.getView, word, ds.toArray.asInstanceOf[Array[Object]]) { }
           }