src/HOL/Mirabelle/Tools/mirabelle_sledgehammer.ML

       val reconstructor = Unsynchronized.ref ""
       val named_thms =
         Unsynchronized.ref (NONE : ((string * locality) * thm list) list option)
       val minimize = AList.defined (op =) args minimizeK
       val metis_ft = AList.defined (op =) args metis_ftK
-      val trivial = Try.invoke_try (SOME try_timeout) pre
+      val trivial = Try.invoke_try (SOME try_timeout) ([], [], []) pre
         handle TimeLimit.TimeOut => false
       fun apply_reconstructor m1 m2 =
         if metis_ft
         then
           if not (Mirabelle.catch_result (reconstructor_tag reconstructor) false