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Only the User and iNetOrgPerson object types have a UserPrincipalName value. Contacts and groups do not.

From

Cover of Microsoft Office 365 Administration Inside Out (Includes Current Book Service), Second Edition

Note

InetOrgPerson was defined in RFC 2798 to represent a standard network user, and many other directory services use it for this purpose. Therefore, inetOrgPerson was brought along to Active Directory so that it would be easier to interoperate with these other products or to migrate them to Active Directory.

https://clintboessen.blogspot.com.au/2010/11/what-are-inetorgperson-objects.html