HTML writer: always output <dt> element, even if it is empty

Fixes #4883

src/Text/Pandoc/Writers/HTML.hs

@@ -830,9 +830,7 @@ blockToHtml opts (OrderedList (startnum, numstyle, _) lst) = do
   return $ foldl (!) l attribs
 blockToHtml opts (DefinitionList lst) = do
   contents <- mapM (\(term, defs) ->
-                  do term' <- if null term
-                                 then return mempty
-                                 else liftM H.dt $ inlineListToHtml opts term
+                  do term' <- liftM H.dt $ inlineListToHtml opts term
                      defs' <- mapM (liftM (\x -> H.dd (x >> nl opts)) .
                                     blockListToHtml opts) defs
                      return $ mconcat $ nl opts : term' : nl opts :

test/Tests/Writers/HTML.hs

@@ -43,4 +43,9 @@ tests = [ testGroup "inline code"
             image "/url" "title" ("my " <> emph "image")
             =?> "<img src=\"/url\" title=\"title\" alt=\"my image\" />"
           ]
+        , testGroup "blocks"
+          [ "definition list with empty <dt>" =:
+            definitionList [(mempty, [para $ text "foo bar"])]
+            =?> "<dl><dt></dt><dd><p>foo bar</p></dd></dl>"
+          ]
         ]