Improve error message in the absence of custom crossref declaration fields

[ddlawton]

I encountered an issue when trying to compile a Quarto document into a pdf. The LaTeX compilation fails with the following error:

Error running filter /Applications/quarto/share/filters/main.lua:
/Applications/quarto/share/filters/main.lua:12672: attempt to concatenate a nil value (local 'env_name')
stack traceback:
        /Applications/quarto/share/filters/main.lua:2824: in function 'metaInjectLatex'
        /Applications/quarto/share/filters/main.lua:12644: in function 'initialize_custom_crossref_categories'
        /Applications/quarto/share/filters/main.lua:23444: in field 'Meta'
        /Applications/quarto/share/filters/main.lua:573: in function 'run_emulated_filter'
        /Applications/quarto/share/filters/main.lua:1334: in local 'callback'
        /Applications/quarto/share/filters/main.lua:1352: in upvalue 'run_emulated_filter_chain'
        /Applications/quarto/share/filters/main.lua:1388: in function </Applications/quarto/share/filters/main.lua:1385>

I have narrowed this env_name problem down to the custom cross-references I have in my yaml head (pasted below). When I remove this section entirely, the pdf will compile. Although given this is a scientific manuscript, I would love to have these custom cross references back!

my yaml header in index.qmd:

---
title: Example manuscript

keywords:
  - key1
  - key2

abstract: |
  this is the abstract

plain-language-summary: |
  this is the plain language summary

key-points: 
  - point1
  - point 2

date: last-modified

crossref:
  custom:
    - kind: float
      key: fig
      reference-prefix: Figure
      space-before-numbering: true
      latex-list-of-description: Figure
    - kind: float
      key: suppfig
      latex-env: suppfig
      reference-prefix: Supplementary Figure 
      space-before-numbering: true
      latex-list-of-description: Supplementary Figure
    - kind: float
      key: tbl
      reference-prefix: Table
      space-before-numbering: true
      latex-list-of-description: Table
    - kind: float
      key: supptbl
      reference-prefix: Supplementary Table
      space-before-numbering: true
      latex-list-of-description: Supplementary Table
      

bibliography: references.bib
csl: citation_style.csl

number-sections: true
---

my _quarto.yml:

project:
  type: manuscript
manuscript:
  article: index.qmd
format:
  html:
    toc: true
    comments:
      hypothesis: true
  docx: default
  jats: default
  pdf:
    documentclass: "article"
    keep-tex: true
notebook-links: global
execute:
  freeze: auto

System details:

1. quarto version: 1.5.57
2. OS: MacOS
3. code editor: vscode

[ddlawton]

Of course after I post this issue i see the potential error -- I missed the latex_env variable for two of my cross reference types.

[cscheid]

We should still offer a better error message than this!