Getting Error: Cannot read property '__payloadclass' of null

I have redis server up and running along with botkit working normally for usermessage functions.
However, I am facing error while using respondToWebhook method. Any help will be greatly appreciated.

The error seems to be generating from this directory location: Bots IPA\Kore ai\BotKit-master\lib\sdk\lib

Here is the detailed Error:
Here are few lines from the error:

Unhandled rejection TypeError: Cannot read property ‘__payloadClass’ of null

at C:\Kore ai\BotKit-master\lib\sdk\lib\requestStore.js:30:54

at tryCatcher (C:\Kore ai\BotKit-master\node_modules\bluebird\js\release\util.js:16:23)

at Promise._settlePromiseFromHandler (C:\Kore ai\BotKit-master\node_modules\bluebird\js\release\promise.js:510:31)