avoid cryptic error message because of internal function not handling null value

news/changelog-1.7.md

@@ -126,16 +126,17 @@ All changes included in 1.7:
 
 ## Other Fixes and Improvements
 
+- A new folder `quarto-session-temp` can be created in `.quarto` to store temporary files created by Quarto during a rendering. Reminder: `.quarto` is for internal use of Quarto and should not be versioned (thus added to `.gitignore`).
+- ([fb38eb5](https://github.com/quarto-dev/quarto-cli/commit/fb38eb56c11e09f44cef58fd3b697ff24bb5a3f3)) Use the `latest` parser for Acorn when analyzing JS code imported from OJS blocks.
 - ([#7260](https://github.com/quarto-dev/quarto-cli/issues/7260)): Add support for `active` class in tabsets so the `.active` tab shows up by default.
 - ([#8613](https://github.com/quarto-dev/quarto-cli/issues/8613)): Fix `giscus` color on load to support dark mode (by @kv9898).
 - ([#11441](https://github.com/quarto-dev/quarto-cli/issues/11441)): Don't add newlines around shortcodes during processing.
 - ([#11643](https://github.com/quarto-dev/quarto-cli/issues/11643)): Improve highlighting of nested code block inside markdown code block, i.e. using ` ```{{python}} ` or ` ```python ` inside ` ````markdown` fenced code block.
-- ([fb38eb5](https://github.com/quarto-dev/quarto-cli/commit/fb38eb56c11e09f44cef58fd3b697ff24bb5a3f3)) Use the `latest` parser for Acorn when analyzing JS code imported from OJS blocks.
 - ([#10532](https://github.com/quarto-dev/quarto-cli/issues/10532)): Quarto changed default of `--headless=old` to `--headless` as [Chrome 132 has removed old headless mode](https://developer.chrome.com/blog/removing-headless-old-from-chrome) and only support new mode. For using old mode, `QUARTO_CHROMIUM` could be set to a [new `chrome-headless-shell` binary](https://developer.chrome.com/blog/chrome-headless-shell) or too an older chrome version (between 128 and 132) and `QUARTO_CHROMIUM_HEADLESS_MODE` set to `old` for using old headless mode with that compatabitle version.
 - ([#10961](https://github.com/quarto-dev/quarto-cli/issues/10961)): Add more information on which Chrome Headless will be used in `quarto check install`. This is helpful to help debug mermaid issues.
+- ([#11606](https://github.com/quarto-dev/quarto-cli/discussions/11606)): Added a new `QUARTO_DOCUMENT_FILE` env var available to computation engine to the name of the file currently being rendered.
+- ([#11803](https://github.com/quarto-dev/quarto-cli/pull/11803)): Added a new CLI command `quarto call`. First users of this interface are the new `quarto call engine julia ...` subcommands.
 - ([#11951](https://github.com/quarto-dev/quarto-cli/issues/11951)): Raw LaTeX table without `tbl-` prefix label for using Quarto crossref are now correctly passed through unmodified.
 - ([#12117](https://github.com/quarto-dev/quarto-cli/issues/12117)): Color output to stdout and stderr is now correctly rendered for `html` format in the Jupyter and Julia engines.
 - ([#12264](https://github.com/quarto-dev/quarto-cli/issues/12264)): Upgrade `dart-sass` to 1.85.1.
-- ([#11803](https://github.com/quarto-dev/quarto-cli/pull/11803)): Added a new CLI command `quarto call`. First users of this interface are the new `quarto call engine julia ...` subcommands.
-- A new folder `quarto-session-temp` can be created in `.quarto` to store temporary files created by Quarto during a rendering. Reminder: `.quarto` is for internal use of Quarto and should not be versioned (thus added to `.gitignore`).
-- ([#11606](https://github.com/quarto-dev/quarto-cli/discussions/11606)): Added a new `QUARTO_DOCUMENT_FILE` env var available to computation engine to the name of the file currently being rendered.
+- ([#12369](https://github.com/quarto-dev/quarto-cli/pull/12369)): `quarto preview` correctly throws a YAML validation error when a `format` key does not conform.

src/command/render/render-contexts.ts

@@ -347,6 +347,11 @@ function mergeQuartoConfigs(
 
   // bibliography needs to always be an array so it can be merged
   const fixupMergeableScalars = (metadata: Metadata) => {
+    // see https://github.com/quarto-dev/quarto-cli/pull/12372
+    // and https://github.com/quarto-dev/quarto-cli/pull/12369
+    // for more details on why we need this check, as a consequence of an unintuitive
+    // ordering of YAML validation operations
+    if (metadata === null) return metadata;
     [
       kBibliography,
       kCss,