fix sending ping with no payload

lib/web/websocket/websocket.js

@@ -594,10 +594,12 @@ class WebSocket extends EventTarget {
    * @param {Buffer|undefined} buffer
    */
   static ping (ws, buffer) {
-    if (!Buffer.isBuffer(buffer)) {
+    if (Buffer.isBuffer(buffer)) {
+      if (buffer.length > 125) {
+        throw new TypeError('A PING frame cannot have a body larger than 125 bytes.')
+      }
+    } else if (buffer !== undefined) {
       throw new TypeError('Expected buffer payload')
-    } else if (buffer.length > 125) {
-      throw new TypeError('A PING frame cannot have a body larger than 125 bytes.')
     }
 
     // An endpoint MAY send a Ping frame any time after the connection is

test/websocket/ping-util.js

@@ -18,10 +18,7 @@ test('ping', async (t) => {
   })
 
   const ws = new WebSocket(`ws://localhost:${wss.address().port}`)
-
-  ws.addEventListener('open', () => {
-    ping(ws, pingBody)
-  })
+  ws.onopen = () => ping(ws, pingBody)
 
   t.after(() => {
     ws.close()
@@ -54,3 +51,25 @@ test('attempting to send invalid ping body', async (t) => {
 
   await completed
 })
+
+test('ping with no payload', async (t) => {
+  const { completed, deepStrictEqual } = tspl(t, { plan: 1 })
+
+  const wss = new WebSocketServer({ port: 0 })
+
+  wss.on('connection', (ws) => {
+    ws.on('ping', (b) => {
+      deepStrictEqual(b, Buffer.alloc(0))
+    })
+  })
+
+  const ws = new WebSocket(`ws://localhost:${wss.address().port}`)
+  ws.onopen = () => ping(ws)
+
+  t.after(() => {
+    ws.close()
+    wss.close()
+  })
+
+  await completed
+})