enable delete files

files.go

@@ -58,6 +58,9 @@ func (b *Files) Get(key string, ns ...string) ([]byte, error) {
 func (b *Files) Set(key string, value []byte, ns ...string) error {
 	namespace := resolveNamespace(ns)
 	dir := path.Join(b.root, namespace)
+	if value == nil {
+		return os.Remove(path.Join(dir, key))
+	}
 	if err := os.MkdirAll(dir, os.ModePerm); err != nil {
 		return err
 	}