${env:VAR:-} with empty default resolves to nil instead of empty string, causing downstream validation failures #14587
Description
Component(s)
confmap
What happened?
Description
Observed Behavior
When using an environment expansion with an empty default:
value: "${env:VAR:-}"and VAR is unset, the resulting value resolves to nil instead of an empty string.
This appears to happen because the envprovider ultimately passes an empty byte slice to NewRetrievedFromYAML, which results in the YAML unmarshaler producing a nil value.
Impact
This leads to validation failures in downstream components that rely on distinguishing between:
- field not set (
nil) - field explicitly set to empty string (
"")
For example, in the attraction processor, validation checks:
if a.Value != nilSince the expanded value becomes nil, the processor treats the field as missing, even though the user explicitly specified it via ${env:VAR:-}.
Expected Behavior
If a user explicitly provides:
value: "${env:VAR:-}"and the default resolves to an empty string, the resolved value should likely be:
""rather than nil, preserving the semantic difference between:
- omitted field
- explicitly empty value
Question
Is nil the intended representation for an empty environment expansion in OTel config?
If not, would it make sense for envprovider to preserve empty defaults as explicit empty strings instead of allowing them to collapse into nil during YAML unmarshaling?
Related
This behavior causes a failure in the contrib repository:
open-telemetry/opentelemetry-collector-contrib#46085
Collector version
Environment information
Environment
OS: Ubuntu 24.04
Compiler: go1.25.7 linux/amd64
OpenTelemetry Collector configuration
receivers:
nop:
processors:
resource/foo:
attributes:
- key: foo
value: "${env:BAR:-}"
action: upsert
exporters:
nop:
service:
pipelines:
metrics:
receivers: [nop]
processors: [resource/foo]
exporters: [nop]Log output
2026-02-14T14:35:01.331Z error service@v0.145.1-0.20260212100729-5a059d1d6718/service.go:165 error found during service initialization {"resource": {"service.instance.id": "f5ffaa7b-1da9-442d-8346-5af7a8ab84aa", "service.name": "otelcontribcol", "service.version": "0.145.0-dev"}, "error": "failed to build pipelines: failed to create \"resource/foo\" processor, in pipeline \"metrics\": error with key \"foo\" (0-th action): error creating AttrProc. Either field \"value\", \"from_attribute\", \"from_context\", or \"default_value\" must be specified"}
go.opentelemetry.io/collector/service.New.func2
go.opentelemetry.io/collector/service@v0.145.1-0.20260212100729-5a059d1d6718/service.go:165
go.opentelemetry.io/collector/service.New
go.opentelemetry.io/collector/service@v0.145.1-0.20260212100729-5a059d1d6718/service.go:232
go.opentelemetry.io/collector/otelcol.(*Collector).setupConfigurationComponents
go.opentelemetry.io/collector/otelcol@v0.145.1-0.20260212100729-5a059d1d6718/collector.go:211
go.opentelemetry.io/collector/otelcol.(*Collector).Run
go.opentelemetry.io/collector/otelcol@v0.145.1-0.20260212100729-5a059d1d6718/collector.go:329
go.opentelemetry.io/collector/otelcol.NewCommand.func1
go.opentelemetry.io/collector/otelcol@v0.145.1-0.20260212100729-5a059d1d6718/command.go:39
github.com/spf13/cobra.(*Command).execute
github.com/spf13/cobra@v1.10.2/command.go:1015
github.com/spf13/cobra.(*Command).ExecuteC
github.com/spf13/cobra@v1.10.2/command.go:1148
github.com/spf13/cobra.(*Command).Execute
github.com/spf13/cobra@v1.10.2/command.go:1071
main.runInteractive
github.com/open-telemetry/opentelemetry-collector-contrib/cmd/otelcontribcol/main.go:72
main.run
github.com/open-telemetry/opentelemetry-collector-contrib/cmd/otelcontribcol/main_others.go:10
main.main
github.com/open-telemetry/opentelemetry-collector-contrib/cmd/otelcontribcol/main.go:63
runtime.main
runtime/proc.go:285
Error: failed to build pipelines: failed to create "resource/foo" processor, in pipeline "metrics": error with key "foo" (0-th action): error creating AttrProc. Either field "value", "from_attribute", "from_context", or "default_value" must be specifiedAdditional context
NOTE: the above config and it's output is replication of bug #46085 from opentelemetry-collector-contrib repo.
issue: issue-url
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