diff --git a/vendor/github.com/spf13/pflag/ip.go b/vendor/github.com/spf13/pflag/ip.go
index 3d414ba..06b8bcb 100644
--- a/vendor/github.com/spf13/pflag/ip.go
+++ b/vendor/github.com/spf13/pflag/ip.go
@@ -16,6 +16,9 @@
 
 func (i *ipValue) String() string { return net.IP(*i).String() }
 func (i *ipValue) Set(s string) error {
+	if s == "" {
+		return nil
+	}
 	ip := net.ParseIP(strings.TrimSpace(s))
 	if ip == nil {
 		return fmt.Errorf("failed to parse IP: %q", s)