Small fixes

Author: dlesbre

src/PatriciaTree.mli

@@ -18,7 +18,7 @@
 (*  See the GNU Lesser General Public License version 2.1                 *)
 (*  for more details (enclosed in the file LICENSE).                      *)
 (**************************************************************************)
-exception Not_found
+
 (** Association maps from key to values, and sets, implemented with
     Patricia Trees, allowing fast merge operations by making use of
     physical equality between subtrees; and custom implementation of

src/functors.ml

@@ -1320,6 +1320,9 @@ module MakeBucketedHeterogeneous
   let set = Array.unsafe_set
 
   let empty = Obj.magic (Array.make Buckets.nb_buckets Map.empty)
+  (* This Obj.magic is required to avoid the '_weak type.
+     It is correct as long as we never mutate empty without copying it first. *)
+  let empty : 'a t = empty
 
   let is_empty arr = Array.for_all Map.is_empty arr
   let cardinal arr = Array.fold_left (fun a b -> a + Map.cardinal b) 0 arr