fix #10: check group length before manipulation

Makefile

@@ -11,7 +11,7 @@ VERSION   = $(shell grep VERSION handler.go | head -1 | cut -d '"' -f2)
 all: buildlocal
 
 buildlocal:
-	go build
+	go build  -o example/example example/example.go
 
 clean:
 	rm -rf $(tool) coverage.out testdata t/out example/example

handler.go

@@ -212,7 +212,7 @@ func (h *Handler) appendAttr(wa map[string]interface{}, a slog.Attr) {
 		}
 		wa[name] = innerwa
 
-		if a.Key != "" {
+		if a.Key != "" && len(h.groups) > 0 {
 			h.groups = h.groups[:len(h.groups)-1]
 		}