Schema validator doesn't recognize Null literals

[SupSuper]

Simple test case, make a schema with "type": "null"
Only the empty value is accepted as valid. The YAML null literals like ~ and null are rejected: https://yaml.org/type/null.html
This should be correctly supported by the parser: https://github.com/mulesoft-labs/yaml-ast-parser/blob/master/src/scalarInference.ts#L71

However, "type": "string" does accept Null literals, so this might be related to this fix: #72

[zallek]

@JPinkney Any updates on that?
As @SupSuper said, the problem might be due to #72 as null token are expected to be parsed as null values and not string according to the YAML spec https://yaml.org/type/null.html
I would suggest reverting this commit

config

unexpected error:

[timo-klarshift]

I am coming from here: redhat-developer/vscode-yaml#277

I forked the yaml-language-server now and added tests for this issue. I also provided a fix which implements this: https://yaml.org/type/null.html

But I am in very doubt, if this will be accepted, as it could be that a lot of implementations actually rely on receiving the Null literals as strings.

So I think the best solution would be to enable some configuration parameter to switch between those behaviors. But recording to the spec, I think the current implementation is just wrong here.

[timo-klarshift]

I created a PR with tests also.
I am not sure if that behavior will break something for the k8s folks.
But in any case, we should stick to the YAML spec :)

#241

[JPinkney]

Yeah, I think this should be switched back to the old behavior. I think in this case the kubernetes schema is actually wrong. If null is allowed in that case then the accepted types should be "string"/"null" not just "string".

Even other validators online that I've found don't allow null when the type is string. When I implemented it originally I just thought they knew something that I didn't so I just figured they were right 🤷‍♂️