src/Pure/General/path.scala

--- a/src/Pure/General/path.scala	Wed Jan 15 19:49:13 2020 +0100
+++ b/src/Pure/General/path.scala	Wed Jan 15 19:54:50 2020 +0100
@@ -233,7 +233,7 @@
         case x => List(x)
       }
 
-    new Path(Path.norm_elems(elems.map(eval).flatten))
+    new Path(Path.norm_elems(elems.flatMap(eval)))
   }
 
   def expand: Path = expand_env(Isabelle_System.settings())