Empty map values are round-tripped to null

[GeorchW]

Description: Empty map values are not round-tripped correctly.

To reproduce:

parseDocument("nothing:").toString()
// expected output: "nothing:"
// actual output:   "nothing: null\n"

Versions:

• Environment: Node.js v16.13.1
• yaml: 2.0.0-10

Additional context

Thanks a lot for this awesome library! I'm using it to edit around in docker-compose files, where the pattern

volumes:
  a-volume:
  another-volume:

is quite common. These are currently round-tripped to

volumes:
  a-volume: null
  another-volume: null

If there is more content after the volumes block, it's getting worse, where this

volumes:
  a-volume:

networks: "whatever"

is round-tripped to this:

volumes:
  a-volume:

    null
networks: "whatever"

There are other minor offenders to round-tripping (like a tiny bit of whitespace preservation here and there), but this is the only offender that is very visible. I can probably refer to the CST for my use-cases, but this might be something you want to look at.

[GeorchW]

I've debugged a little and I believe I found the culprit:

yaml/src/schema/common/null.ts

Lines 11 to 12 in 7998a95

	stringify: ({ source }, ctx) =>
	source && nullTag.test.test(source) ? source : ctx.options.nullStr

When the null tag is stringified, it checks if the source contains something that would be parsed as null before writing it out. I'm not sure if that's neccessary, I don't know what scenarios there are where the source attribute is not containing a string that parses to null, that's where I'm not deep enough in the code.

[GeorchW]

Wow, that was fast -- thanks a lot!

[eemeli]

You're right, that shouldn't have been happening. The test in stringify was wrong, as it didn't recognise source === '' as a valid representation of a null value.

[GeorchW]

How is the release schedule?

[eemeli]

There's no schedule as such. I'll try and roll out a new release within a week or two; there are a few other fixes I'd like to include.

[GeorchW]

Okay, thanks again!