[pkg/stanza] json null value handling

[newly12]

Component(s)

pkg/stanza

What happened?

Description

json null value handling and processing is incorrect.

Steps to Reproduce

given the input like {"empty": null} and json_parser enabled.

Expected Result

empty type

Actual Result

https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/pkg/stanza/adapter/converter.go#L326

by default given nil it returns fmt.Sprintf("%v", nil), which is "<nil>"(string)

     -> empty: Str(<nil>)

Collector version

latest

Environment information

Environment

OS: (e.g., "Ubuntu 20.04")
Compiler(if manually compiled): (e.g., "go 14.2")

OpenTelemetry Collector configuration

No response

Log output

No response

Additional context

No response

[github-actions]

Pinging code owners:

• pkg/stanza: @djaglowski

See Adding Labels via Comments if you do not have permissions to add labels yourself.