handle empty message (ping) in ws

app/javascript/mastodon/stream.js

@@ -74,7 +74,10 @@ export default function getStream(streamingAPIBaseURL, accessToken, stream, { co
   const ws = new WebSocketClient(`${streamingAPIBaseURL}/api/v1/streaming/?${params.join('&')}`);
 
   ws.onopen      = connected;
-  ws.onmessage   = e => received(JSON.parse(e.data));
+  ws.onmessage   = e => {
+    if (e.data !== '')
+      received(JSON.parse(e.data));
+  }
   ws.onclose     = disconnected;
   ws.onreconnect = reconnected;