nullCache :: Monad m => Cache m k a
nullCache = Cache
    { readCache      = \_   -> return Nothing
    , writeCache     = \_ _ -> return False  -- always full!
    , clearCache     =         return ()
    , clearFromCache = \_   -> return ()
    }
nullCache :: Monad m => Cache m k a
nullCache = Cache
    { readCache      = \_   -> return Nothing
    , writeCache     = \_ _ -> return False  -- always full!
    , clearCache     =         return ()
    , clearFromCache = \_   -> return ()
    }
nullCache = Cache
    { readCache      = \_   -> return Nothing
    , writeCache     = \_ _ -> return False  -- always full!
    , clearCache     =         return ()
    , clearFromCache = \_   -> return ()
    }