diff --git a/userdata.go b/userdata.go
index bd3e28aa1d..8d2eff9f74 100644
--- a/userdata.go
+++ b/userdata.go
@@ -21,6 +21,9 @@ func (d *userData) Set(key string, value interface{}) {
 			return
 		}
 	}
+	if value == nil {
+		return
+	}
 
 	c := cap(args)
 	if c > n {