I want transfer vert weights (by name) from Source mesh to Target mesh with 'Data transfer' modifier.
If source object has +1 additional vertex group compared to Target, the vertex group transfer will fail for all vertices groups.

Example blend file - as soon as user deletes 'DeleteMe!' vertex group from source mesh, the vertex group transfer will work ok.

I wish 'Data transfer' modifier, would just skip extra groups (or automatically add it to target). Example is easy, but if you had 100 vertex groups it would be hard to find problematic vert group.