Basic Joins : Exception while exporting the aggregation to JAVA

While running Basic Joins Session, I was trying to export the pipeline created via Compass to JAVA Code, however I am getting below Error in Compass

Unrecognized option to $lookup: let

Kindly advise why ?

feel free to use the search by the forum, there is already a topic related to this issue Chapter 2: $lookup Export to Language using Compass