otelslog: Transform nil attribute to empty log.Value (#6246)

Fixes
#6242

CHANGELOG.md

@@ -12,6 +12,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 - Transform nil attribute values to `log.Value` zero value instead of panicking in `go.opentelemetry.io/contrib/bridges/otellogrus`. (#6237)
 - Transform nil attribute values to `log.Value` zero value instead of panicking in `go.opentelemetry.io/contrib/bridges/otelzap`. (#6237)
+- Transform nil attribute values to `log.Value` zero value instead of `log.StringValue("<nil>")` in `go.opentelemetry.io/contrib/bridges/otelslog`. (#6246)
 
 <!-- Released section -->
 <!-- Don't change this section unless doing release -->

bridges/otelslog/handler.go

@@ -26,8 +26,9 @@
 //
 // Attribute values are transformed based on their [slog.Kind]:
 //
-//   - [slog.KindAny] are transformed to [log.StringValue]. The value is
+//   - [slog.KindAny] non-nil values are transformed to [log.StringValue]
 //     encoded using [fmt.Sprintf].
+//     Nil values are transformed to a zero value of [log.Value].
 //   - [slog.KindBool] are transformed to [log.BoolValue] directly.
 //   - [slog.KindDuration] are transformed to [log.Int64Value] as nanoseconds.
 //   - [slog.KindFloat64] are transformed to [log.Float64Value] directly.
@@ -411,6 +412,9 @@ func (b *kvBuffer) AddAttr(attr slog.Attr) bool {
 func convertValue(v slog.Value) log.Value {
 	switch v.Kind() {
 	case slog.KindAny:
+		if v.Any() == nil {
+			return log.Value{}
+		}
 		return log.StringValue(fmt.Sprintf("%+v", v.Any()))
 	case slog.KindBool:
 		return log.BoolValue(v.Bool())

bridges/otelslog/handler_test.go

@@ -240,6 +240,7 @@ func TestSLogHandler(t *testing.T) {
 					"string", "str",
 					"time", now,
 					"uint64", uint64(3),
+					"nil", nil,
 					// KindGroup and KindLogValuer are left for slogtest.TestHandler.
 				)
 			},
@@ -254,6 +255,7 @@ func TestSLogHandler(t *testing.T) {
 				hasAttr("string", "str"),
 				hasAttr("time", now.UnixNano()),
 				hasAttr("uint64", int64(3)),
+				hasAttr("nil", nil),
 			}},
 		},
 		{