fix profilingDetail errors when enabling profiling (#493)

Author: yorickvP

modules/plan.nix

@@ -149,7 +149,7 @@ let
     };
 
     profilingDetail = mkOption {
-      type = nullOr str;
+      type = nullOr uniqueStr;
       default = (def.profilingDetail or "exported-functions");
     };