Tianhao Guo

fix an edge case bug that "identity_policies" is nil

2

Fixes #17006 client side: check if "identity_policies" is nil, goto DONE, then cli `vault login` will not return unexpected error. server side: check if key `out.NamespaceID` exists in the map...

**Describe the bug** `vault login ` failed with error: ```sh ~ % vault login hvs.CAESINdDxxx Error authenticating: error accessing token policies: unable to convert identity policies to expected format ```...