diff --git a/pkg/credentialplugin/reader/reader.go b/pkg/credentialplugin/reader/reader.go
index 6ffdfd7f..9ba94f5d 100644
--- a/pkg/credentialplugin/reader/reader.go
+++ b/pkg/credentialplugin/reader/reader.go
@@ -22,6 +22,8 @@ type Interface interface {
 
 type Reader struct{}
 
+// Read parses the environment variable KUBERNETES_EXEC_INFO.
+// If the environment variable is not given by kubectl, Read returns a zero value.
 func (r Reader) Read() (credentialplugin.Input, error) {
 	execInfo := os.Getenv("KUBERNETES_EXEC_INFO")
 	if execInfo == "" {
diff --git a/pkg/credentialplugin/types.go b/pkg/credentialplugin/types.go
index dd044c54..0b2c7710 100644
--- a/pkg/credentialplugin/types.go
+++ b/pkg/credentialplugin/types.go
@@ -4,6 +4,7 @@ package credentialplugin
 import "time"
 
 // Input represents an input object of the credential plugin.
+// This may be a zero value if the input is not available.
 type Input struct {
 	ClientAuthenticationAPIVersion string
 }
diff --git a/pkg/credentialplugin/writer/credential_plugin.go b/pkg/credentialplugin/writer/credential_plugin.go
index 6ac8c81c..5dd32483 100644
--- a/pkg/credentialplugin/writer/credential_plugin.go
+++ b/pkg/credentialplugin/writer/credential_plugin.go
@@ -40,7 +40,7 @@ func (w *Writer) Write(out credentialplugin.Output) error {
 
 func generateExecCredential(out credentialplugin.Output) (any, error) {
 	switch out.ClientAuthenticationAPIVersion {
-	// Default to v1beta1 if KUBERNETES_EXEC_INFO is not available
+	// If the API version is not available, fall back to v1beta1.
 	case clientauthenticationv1beta1.SchemeGroupVersion.String(), "":
 		return &clientauthenticationv1beta1.ExecCredential{
 			TypeMeta: metav1.TypeMeta{