chore: extra annotations logs (#1549)

Co-authored-by: rongxin <alinsran@apache.org>
diff --git a/pkg/providers/ingress/translation/annotations/upstreamscheme/upstreamscheme.go b/pkg/providers/ingress/translation/annotations/upstreamscheme/upstreamscheme.go
index 2e183c4..f9ce46b 100644
--- a/pkg/providers/ingress/translation/annotations/upstreamscheme/upstreamscheme.go
+++ b/pkg/providers/ingress/translation/annotations/upstreamscheme/upstreamscheme.go
@@ -30,6 +30,9 @@
 
 func (w *upstreamscheme) Parse(e annotations.Extractor) (interface{}, error) {
 	scheme := strings.ToLower(e.GetStringAnnotation(annotations.AnnotationsUpstreamScheme))
+	if scheme == "" {
+		return nil, nil
+	}
 	_, ok := apisixv1.ValidSchemes[scheme]
 	if ok {
 		return scheme, nil