One-line examples with a judgement are unprocessible when producing an HTML file

[CLRafaelR]

I am trying to produce an HTML file which contains one-line examples with a judgement. If I correctly understand, the following markdown syntax will work:

::: ex
^* This traditionally signals ungrammaticality.
:::

However, pandoc throws an error on lua when processing the markdown file, as follows:

Error running filter configuration/pandoc-ling/pandoc-ling.lua:
configuration/pandoc-ling/pandoc-ling.lua:607: attempt to index a nil value (field '?')
stack traceback:
	configuration/pandoc-ling/pandoc-ling.lua:607: in function 'pandocMakeSingle'
	configuration/pandoc-ling/pandoc-ling.lua:527: in function 'pandocMakeExample'
	configuration/pandoc-ling/pandoc-ling.lua:256: in function 'processDiv'
Error: pandoc document conversion failed with error 83

The problem looks similar to the issue on the following link, but I cannot work around by myself since I am not familiar with lua...
https://stackoverflow.com/q/12153537/10215301

What am I missing...?

MWE

Here I put an Rmarkdown example with its subsidiary R packages, bookdown. The contents are exactly same as pandoc's markdown, except what I wrote in YAML section.

---
author: Masataka OGAWA
title: Using pandoc-ling for HTML

output: 
  bookdown::html_document2:
    pandoc_args:
      - --lua-filter=configuration/pandoc-ling/pandoc-ling.lua

  ## No problem with pdf-producing
  bookdown::pdf_document2:
    pandoc_args:
      - --lua-filter=configuration/pandoc-ling/pandoc-ling.lua
---

These two examples throw an error when I produce an HTML file:

```
Error running filter configuration/pandoc-ling/pandoc-ling.lua:
configuration/pandoc-ling/pandoc-ling.lua:607: attempt to index a nil value (field '?')
stack traceback:
	configuration/pandoc-ling/pandoc-ling.lua:607: in function 'pandocMakeSingle'
	configuration/pandoc-ling/pandoc-ling.lua:527: in function 'pandocMakeExample'
	configuration/pandoc-ling/pandoc-ling.lua:256: in function 'processDiv'
Error: pandoc document conversion failed with error 83
```

::: ex
^* This traditionally signals ungrammaticality.
:::

::: ex
a. ^* This traditionally signals ungrammaticality.
:::

<!-- 

This commented-out example works fine.

::: ex

a. ^* This traditionally signals ungrammaticality.
d. However, such long sequences sometimes lead to undesirable effects in the layout.

:::

-->    

Note but that I can produce a PDF file without any problem with the Rmd file above, as shown in the following screen capture.

Environment

Environment
pandoc-ling: v1.4
pandoc: v2.11.4
OS: Windows 10 x64 (build 19042)

[cysouw]

You found a bug! It's fixed now in the master branch, so please download it from there. The next release will come later.

[CLRafaelR]

I always appreciate your quick response and now I confirm that I can get the desirable HTML!
Thank you so much and I close this issue!