pandoc-2.19: test/command/8155.md

```
% pandoc -f native -t revealjs
[ Null
, Header
    2
    ( "header-after-null" , [] , [] )
    [ Str "Header"
    , Space
    , Str "after"
    , Space
    , Str "null"
    ]
]
^D
<section id="header-after-null" class="title-slide slide level2">
<h2>Header after null</h2>

</section>
```