Merge into with multiple updates and inserts

Maybe I'm missing something but

The error message complains you can't have multiple WHEN MATCHED so you could convert

WHEN MATCHED AND TARGET.NodeId = Source.StartNodeId THEN    UPDATE SET TARGET.NodeId = SOURCE.StartNodeId,               TARGET.LinkId = SOURCE.IdWHEN MATCHED AND TARGET.NodeId = Source.EndNodeId THEN    UPDATE SET TARGET.NodeId = SOURCE.EndNodeId,               TARGET.LinkId = SOURCE.Id

to

WHEN MATCHED AND TARGET.NodeId IN (Source.StartNodeId,Source.EndNodeId) THEN    UPDATE SET TARGET.NodeId = CASE                                  WHEN TARGET.NodeId = Source.StartNodeId                                  THEN SOURCE.StartNodeId                                  ELSE Source.EndNodeId                                END,               TARGET.LinkId = SOURCE.Id

But as the first branch of the CASE is hit when TARGET.NodeId = Source.StartNodeId and also sets TARGET.NodeId = Source.StartNodeId and similarly for the second branch then that seems to simplify to

WHEN MATCHED AND TARGET.NodeId IN (Source.StartNodeId,Source.EndNodeId) THEN    UPDATE SET TARGET.LinkId = SOURCE.Id