fix: ignore empty json strings for locale (#678)

* Revert "fix: ignore all unmarshal errors from locale (#673)"

This reverts commit fbf009fe75.

* fix: ignore empty json strings for locale

pkg/oidc/types.go

@@ -3,6 +3,7 @@ package oidc
 import (
 	"database/sql/driver"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"reflect"
 	"strings"
@@ -77,16 +78,25 @@ func (l *Locale) MarshalJSON() ([]byte, error) {
 }
 
 // UnmarshalJSON implements json.Unmarshaler.
-// All unmarshal errors for are ignored.
-// When an error is encountered, the containing tag will be set
+// When [language.ValueError] is encountered, the containing tag will be set
 // to an empty value (language "und") and no error will be returned.
 // This state can be checked with the `l.Tag().IsRoot()` method.
 func (l *Locale) UnmarshalJSON(data []byte) error {
-	err := json.Unmarshal(data, &l.tag)
-	if err != nil {
-		l.tag = language.Tag{}
+	if len(data) == 0 || string(data) == "\"\"" {
+		return nil
 	}
-	return nil
+	err := json.Unmarshal(data, &l.tag)
+	if err == nil {
+		return nil
+	}
+
+	// catch "well-formed but unknown" errors
+	var target language.ValueError
+	if errors.As(err, &target) {
+		l.tag = language.Tag{}
+		return nil
+	}
+	return err
 }
 
 type Locales []language.Tag