src/Pure/System/isabelle_system.scala

--- a/src/Pure/System/isabelle_system.scala	Tue Sep 21 00:20:55 2021 +0200
+++ b/src/Pure/System/isabelle_system.scala	Tue Sep 21 11:23:18 2021 +0200
@@ -139,7 +139,8 @@
 
   def isabelle_name(): String = getenv_strict("ISABELLE_NAME")
 
-  def identification(): String = "Isabelle/" + isabelle_id() + isabelle_heading()
+  def identification(): String =
+    "Isabelle" + (try { "/" + isabelle_id () } catch { case ERROR(_) => "" }) + isabelle_heading()
 
 
   /** file-system operations **/