src/HOL/Tools/Nitpick/nitpick_scope.ML

     case (if null cards then [] else ["card: " ^ commas (map implode cards)]) @
          (if null maxes then [] else ["max: " ^ commas (map implode maxes)]) @
          (if null iters then [] else ["iter: " ^ commas (map implode iters)]) @
          miscs of
       [] => "empty"
-    | lines => space_implode "\n" lines
+    | lines => cat_lines lines
   end
 
 fun scopes_equivalent (s1 : scope, s2 : scope) =
   #datatypes s1 = #datatypes s2 andalso #card_assigns s1 = #card_assigns s2
 fun scope_less_eq (s1 : scope) (s2 : scope) =