@@ -413,8 +413,8 @@ convertWithOpts opts = do
413413 mconcat <$> mapM (readFile' >=> r readerOpts) sources
414414
415415 metadata <- if format == "jats" &&
416− lookup "csl" (optMetadata opts) == Nothing &&
417− lookup "citation-style" (optMetadata opts) == Nothing
416+ isNothing (lookup "csl" (optMetadata opts)) &&
417+ isNothing (lookup "citation-style" (optMetadata opts))
418418 then do
419419 jatsCSL <- readDataFile datadir "jats.csl"
420420 let jatsEncoded = makeDataURI ("application/xml", jatsCSL)