SAP Message RSAN_WB041 - Source &1 for join &2 does not have any fields. Maintenance not possible

Diagnosis
The source node &V1& does not provide any fields for join node &V2&.

System Response
It is not possible to maintain a join relationship.

Procedure
First maintain the fields in source node &V1& or in one of itspredecessor nodes, and then maintain the join node.