diff -r 4123fca23296 -r ef8c9b3d5355 src/Pure/PIDE/document.scala
--- a/src/Pure/PIDE/document.scala	Thu Mar 04 15:49:15 2021 +0100
+++ b/src/Pure/PIDE/document.scala	Thu Mar 04 15:52:08 2021 +0100
@@ -1027,7 +1027,7 @@
         if (execs.isDefinedAt(exec_id)) None else Some(exec_id -> st)
 
       val (changed_commands, new_execs) =
-        update.foldLeft((Nil: List[Command], execs)) {
+        update.foldLeft((List.empty[Command], execs)) {
           case ((commands1, execs1), (command_id, exec)) =>
             val st = the_static_state(command_id)
             val command = st.command