Running through the "hello world" example for quarto books shows an error message now, whereas it didn't a few weeks ago. Everything still seems to work fine though.

```
quarto create-project mybook --type book
cd mybook
quarto preview
```
gives output:
```
Creating project at /Users/tomasz/mybook:
  - Created _quarto.yml
  - Created .gitignore
  - Created .gitattributes
  - Created index.qmd
  - Created intro.qmd
  - Created summary.qmd
  - Created references.qmd
  - Created cover.png
  - Created references.bib
Preparing to preview
[1/4] index.qmd
[2/4] intro.qmd
[3/4] summary.qmd
[4/4] references.qmd

Watching files for changes
Browse at http://localhost:6733/
ERROR: Error: Executed file not found for book item: intro.qmd
GET: /
ERROR: Error: Executed file not found for book item: index.qmd
GET: /intro.html
ERROR: Error: Executed file not found for book item: index.qmd
GET: /summary.html
ERROR: Error: Executed file not found for book item: index.qmd
GET: /references.html
```
2021-12-07T22:06:27Z
t-kalinowski
closed
Error message from quarto preview
https://github.com/quarto-dev/quarto-cli/issues/206