Announcement: Azure Logic Apps' New Data Mapper for Visual Studio Code (Preview)

SwapnilBankar good question regarding null value in JSON output. I know part of the answer and I will have to get back with the remaining part. 

The map code that you see when you save the map (.lml file) has reserved keywords - one of them is $null. When you wish to assign the value of an output node to null in case of JSON, it could be assigned to $null. In case of XML, the equivalent is $nil. 

I think any function that takes a constant value input, you can type the value to be null in the properties pane. One scenario could be to use If or If-else function. Based upon the condition evaluation, you may want to assign the output to null in case of a JSON output. (nil in case of XML). For user convenience, we do internal check as well and convert null/nil to match the JSON and XML requirements. As a user you can use either null or nil across JSON and XML if that is more convenient for you. Just type the value to be null or nill and you can validate the code view to see $null or $nil in the side by side view. 

The picture below may help. Specifically look for red-boxed elements: