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GetFieldValue returns string "null" for null field value #6317
Description
What happened?
GetFieldValue returns a string value "null" when a yaml field is null. There is no way to differentiate between the 2 cases based on the return value, for example to check if a field of a different expected type is null or has an incorrect type.
What did you expect to happen?
I expected nil to be returned in that case.
How can we reproduce it (as minimally and precisely as possible)?
package main
import (
"fmt"
"strings"
"sigs.k8s.io/kustomize/kyaml/kio"
"sigs.k8s.io/kustomize/kyaml/yaml"
)
const input = `
kind: TestKind
metadata:
name: hello-world
spec:
fieldWithNullValue: null
fieldWithStringNullValue: "null"
`
func main() {
data, err := kio.ParseAll(input)
if err != nil {
fmt.Println("error: ", err)
return
}
checkFieldValue(data[0], "spec", "fieldWithNullValue")
checkFieldValue(data[0], "spec", "fieldWithStringNullValue")
}
func checkFieldValue(node *yaml.RNode, fieldPath ...string) {
rNode, err := node.Pipe(yaml.Lookup(fieldPath...))
if err != nil {
fmt.Println("error: ", err)
return
}
fullPath := strings.Join(fieldPath, ".")
if rNode == nil {
fmt.Println("field not found: ", fullPath)
return
}
fmt.Println(fmt.Sprintf("%s tag: %s, value: %q", fullPath, rNode.YNode().Tag, rNode.YNode().Value))
f, err := node.GetFieldValue(fullPath)
if err != nil {
fmt.Println("error: ", err)
return
}
fmt.Println(fmt.Sprintf("%s type: %T, value: %q", fullPath, f, f))
}Expected output
spec.fieldWithNullValue tag: !!null, value: "null"
spec.fieldWithNullValue type: <nil>, value: %!q(<nil>)
spec.fieldWithStringNullValue tag: !!str, value: "null"
spec.fieldWithStringNullValue type: string, value: "null"Actual output
spec.fieldWithNullValue tag: !!null, value: "null"
spec.fieldWithNullValue type: string, value: "null"
spec.fieldWithStringNullValue tag: !!str, value: "null"
spec.fieldWithStringNullValue type: string, value: "null"Kustomize version
sigs.k8s.io/kustomize/kyaml v0.21.1
Operating system
Windows
Activity
kubernetes-prow commentedon Oct 8, 2026
This issue is currently awaiting triage.
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tal-sapan commentedon Oct 8, 2026
The solution is probably to add handlng for the null case here:
kustomize/kyaml/yaml/rnode.go
Line 1358 in 5d465f7