Post request fails.

[JyotiDubey]

For all post requests(which are not even concurrent) the error comes as
NoSuchMethodError: The method 'openUrl' was called on null.
Receiver: null
Tried calling: openUrl("POST", Instance of '_SimpleUrl
Request type: var response = await twitterClient.request("POST", "statuses/update.json",body: {"status":"some test"});

Any change that needs to be made in the request?