diff -r c3f07c950116 -r db9c6be8e236 src/Pure/PIDE/headless.scala
--- a/src/Pure/PIDE/headless.scala	Tue Mar 05 15:58:45 2024 +0100
+++ b/src/Pure/PIDE/headless.scala	Tue Mar 05 16:06:06 2024 +0100
@@ -448,7 +448,7 @@
     def apply(
       options: Options,
       session_background: Sessions.Background,
-      log: Logger = No_Logger
+      log: Logger = new Logger
     ): Resources = new Resources(options, session_background, log = log)
 
     def make(
@@ -457,7 +457,7 @@
       session_dirs: List[Path] = Nil,
       include_sessions: List[String] = Nil,
       progress: Progress = new Progress,
-      log: Logger = No_Logger
+      log: Logger = new Logger
     ): Resources = {
       val session_background =
         Sessions.background(options, session_name, dirs = session_dirs,
@@ -605,7 +605,7 @@
   class Resources private[Headless](
     val options: Options,
     session_background: Sessions.Background,
-    log: Logger = No_Logger)
+    log: Logger = new Logger)
   extends isabelle.Resources(session_background.check_errors, log = log) {
     resources =>