Add dummy for a missing IO specialisation

Author: jeltsch

src/Database/LSMTree.hs

@@ -108,6 +108,7 @@ module Database.LSMTree (
   , SerialiseValue
 
     -- * Monoidal value resolution
+  , dummy
   , ResolveValue (..)
   , resolveDeserialised
     -- ** Properties
@@ -602,6 +603,9 @@ supplyUnionCredits (Internal.Table' t) (UnionCredits credits) =
   Monoidal value resolution
 -------------------------------------------------------------------------------}
 
+dummy :: Monad m => m ()
+dummy = return ()
+
 -- | A class to specify how to resolve/merge values when using monoidal updates
 -- ('Mupsert'). This is required for merging entries during compaction and also
 -- for doing lookups, resolving multiple entries of the same key on the fly.