Unexpected exception is thrown while reading source field

When creating mapping "many to one" with some transformation, the processing of the mapping in camel route throws following error:

io.atlasmap.api.AtlasException: Errors: [Unexpected exception is thrown while reading source field: null: docId='null', path='null'],

Attached the mapping file and

Using the Atlasmap master branch (version 2.1.0-SNAPSHOT)