Content modifier: unable to use arrays as a value

[psmolkin]

Bug Report

I found that using a YAML array of strings as a value is not supported or not implemented via content_modifier precessor:

To Reproduce

service:
  log_Level: debug
pipeline:
  inputs:
    - name: dummy
      dummy: '{"message": "hello world"}'
      processors:
        logs:
          - name: opentelemetry_envelope
          - name: content_modifier
            context: otel_resource_attributes
            action: insert
            key: loki.resource.labels
            value:
              - bar
              - baz
  outputs:
    - name : stdout
      match: '*'
      format: json

The config above leads to the following errors:

[2025/10/20 11:37:39.2824548] [debug] [processor] no condition set for processor unit (pu=content_modifier)
[2025/10/20 11:37:39.2860649] [debug] [processor:content_modifier:content_modifier.0] [action: insert] failed to insert key: loki.resource.labels
[2025/10/20 11:37:39.2880649] [ warn] [processor] failed to process chunk
[{"date":1760974658.002465,"__internal__":{"group_attributes":{"resource":{"attributes":{}},"scope":{}},"log_metadata":{}},"message":"hello world"}]

Expected behavior
OTEL Collector supports that:

  config:
    receivers:
      otlp/debug:
        protocols:
          grpc: null
          http:
            endpoint: 0.0.0.0:4319
    processors:
      resource/debug:
        attributes:
          - action: insert
            key: loki.resource.labels
            value:
              - bar
              - baz
    exporters:
      debug:
        verbosity: detailed
    service:
      pipelines:
        logs/debug:
          receivers: [otlp/debug]
          processors: [resource/debug]
          exporters: [debug]

output:

ResourceLog #5
Resource SchemaURL:
Resource attributes:
    -> loki.resource.labels: Slice(["bar","baz"])
ScopeLogs #0

Your Environment

• Version used: 4.1.1