config: Handle null attributes as invalid

[pellared]

null attribute should be considered as an invalid input for ParseYAML (and when parsing JSON as well) as we already have test cases like invalid nil value.

Originally posted by @pellared in #6603

CC @codeboten

[mikeblum]

Can I pick this up? @pellared

[mikeblum]

After digging pretty deeply into the YAML spec its unclear to me if we want to be writing custom parsers to error on different cases such as:

attr: null
attr: []
attr: 0
attr:

map:
  -

imo the current behaviour of parseYAML ignoring these attributes entirely is correct but I defer to @pellared on what the correct behavious should be.

[pellared]

We should consistently "ignore" invalid values or return an error. I think that if something is not compliant with the scheme then it should return an error.

Moreover, from https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/configuration/sdk.md#parse:

Parse SHOULD return an error if [...] The parsed file content does not conform to the configuration model schema.

its unclear to me if we want to be writing custom parsers to error on different cases such as:

This is my expectation.

[MrAlias]

its unclear to me if we want to be writing custom parsers to error on different cases such as:

This is my expectation.

Wouldn't this mean we would completely rewrite a yaml parsing library? That does not seem like something we want to maintain.

[pellared]

Wouldn't this mean we would completely rewrite a yaml parsing library?

I mean add additional validation which is unfortunately not handled by github.com/atombender/go-jsonschema. It should not be a rewrite. It seems we already doing it in config_json.go and config_yaml.go.

However, probably it would be a lot better to contribute to https://github.com/omissis/go-jsonschema (or at least create issues).