Do not alloc multiple noop exporters (#5083)

sdk/log/exporter.go

@@ -41,6 +41,8 @@ type Exporter interface {
 	ForceFlush(ctx context.Context) error
 }
 
+var defaultNoopExporter = &noopExporter{}
+
 type noopExporter struct{}
 
 func (noopExporter) Export(context.Context, []Record) error { return nil }

sdk/log/simple.go

@@ -27,7 +27,7 @@ type SimpleProcessor struct {
 func NewSimpleProcessor(exporter Exporter) *SimpleProcessor {
 	if exporter == nil {
 		// Do not panic on nil exporter.
-		exporter = noopExporter{}
+		exporter = defaultNoopExporter
 	}
 	return &SimpleProcessor{exporter: exporter}
 }