Docs feedback: loki.process labels values don't support empty strings

[jameshartig]

URL

https://grafana.com/docs/alloy/latest/reference/components/loki/loki.process/

Feedback

The docs suggest you can set an empty value in the values key/value map but that's not actually supported by the code.

stage.labels {
    values = {
      env  = "",         // Sets up an 'env' label, based on the 'env' extracted value.
      user = "username", // Sets up a 'user' label, based on the 'username' extracted value.
    }
}

The above code snippet from the docs suggest that an empty value implies using the key but the code does not do that. See https://github.com/grafana/alloy/blob/1881ae4ee9b1d4fb3fa575902eb6287b53720c82/internal/component/loki/process/stages/labels.go#L71 and https://github.com/grafana/alloy/blob/1881ae4ee9b1d4fb3fa575902eb6287b53720c82/internal/component/loki/process/stages/structured_metadata.go#L50.

I would expect those to check for the value being empty but they're not.

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