When migration from group manager the username in the luckperms_player will be always null.
But in the groupmanager user.yml config there is a key called lastname , it would be great if that key can be used if it's present.

Example

  34a444ce-6b4b-3f1e-8b2c-23294f653cd4:
    lastname: voodootje0
    group: Owner
    subgroups: []
    permissions: []