diff --git a/lib/validate.js b/lib/validate.js
index 5131a3ab..a95d708f 100644
--- a/lib/validate.js
+++ b/lib/validate.js
@@ -72,6 +72,7 @@ addMethod(string, 'ws', function (schemas, msg = 'invalid websocket') {
     name: 'ws',
     message: msg,
     test: value => {
+      if (!value) return true
       try {
         // eslint-disable-next-line no-new
         new URL(value)