Unexpected output when deleting maps

[AbrohamLincoln]

Describe the bug
If you delete all maps from a yaml document, the output is improperly formatted if the original document contains a document start.

Version of yq: v4.40.5
Operating system: mac
Installed via: homebrew

Input Yaml
test.yml:

---
foo:
  bar: baz

Command

yq 'del(.foo)' test.yaml

Actual behavior

---
{}

Expected behavior

---

or

or

{}

Additional context
I need to handle a case where I might delete all of the maps in a doc, but not always. The doc may or may not have the document start line.
The workaround I've come up with is to output as json, which drops the document start and the comments, then convert it back to yaml.

yq 'del(.foo)' test.yaml -o json | yq -p json -o yaml

which results in the following:

{}

Related to: #493

[mikefarah]

yq purposefully keeps the document separator and any comments by default. To get rid of document separators you can use the "--no-doc" flag.

yq 'del(.foo)' --no-doc test.yaml

[AbrohamLincoln]

Is there a different way to perform the delete that wont result in an empty map?
I wouldn't mind (and honestly expected) having just the document separator or an empty string as the output.

[mikefarah]

Hmm yeah - you could apply another update if the length of the map is 0. Some thing like:

yq 'del(.foo) | select(length == 0) |= ""' test.yaml
---

So after ".foo" is deleted, if the map length is 0 (has no kids), we can set it to the empty string

[AbrohamLincoln]

Thanks!