How to change Send Button to Enabled in ChatInputBar?

I have followed this example to create my customized xib
https://github.com/badoo/Chatto/issues/148

However the SendButton is still link to ChatInputBar, and in the class I noticed that to updateSendButton is actually fileprivate
`fileprivate func updateSendButton() {
self.sendButton.isEnabled = self.shouldEnableSendButton(self)
}`

How to I edit the sendButton to change to Enabled manually at my own viewController?

Start with ChatInputBar and its fileprivate updateSendButton implementation, then compare the customized XIB from issue #148 with the view controller integration. Confirm the supported way to control the send button's enabled state and make the behavior clear for customized ChatInputBar views.

Written by the indexing model from the issue text.