When repairing logger roles exception

[FriedRice-Mao]

Fix: https://github.com/casbin/node-casbin/issues/327

When repairing printRoles(), n is' Roles [Map] {} ', resulting in printing failure

[casbin-bot]

@Gabriel-403 @Zxilly @kingiw @nodece please review

[hsluoyz]

@gensir plz fix:

[hsluoyz]

@gensir plz fix:

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}