{"error":{"code":"","message":"Value cannot be null.\r\nParameter name: source"}}

I am trying to use the reference service https://services.odata.org/TripPinRESTierService form Salesforce, and the Airlines and Airports works well. But when I try to access the Person Object, I get this error:

{"error":{"code":"","message":"Value cannot be null.\r\nParameter name: source"}}

This is the query that is being made.

https://services.odata.org/TripPinRESTierService/(S(y5p3g0acttyshhhmucgq5fvb))/People?$filter=UserName eq 'angelhuffman'&$count=true&$select=AddressInfo,Age,Emails,FavoriteFeature,Features,FirstName,Gender,HomeAddress,LastName,MiddleName,UserName

I am assuming the primary key of that object is the Username.