Cannot convert null literal to non-nullable reference type.

Nullability of reference types in return type of 'Task<PostalInformationResponse?> GrarClient.GetPostalInformation(string postcode)' doesn't match implicitly implemented member 'Task<PostalInformationResponse> IGrarClient.GetPostalInformation(string postcode)'.

'Contactgegevens.Empty' hides inherited member 'ReadOnlyCollection<Contactgegeven>.Empty'. Use the new keyword if hiding was intended.

'Postnamen.Empty' hides inherited member 'ReadOnlyCollection<Postnaam>.Empty'. Use the new keyword if hiding was intended.

'Datum' defines 'Equals' but not 'GetHashCode'

'HoofdactiviteitenVerenigingsloket.Empty' hides inherited member 'ReadOnlyCollection<HoofdactiviteitVerenigingsloket>.Empty'. Use the new keyword if hiding was intended.

'Locaties.Empty' hides inherited member 'ReadOnlyCollection<Locatie>.Empty'. Use the new keyword if hiding was intended.

'Vertegenwoordigers.Empty' hides inherited member 'ReadOnlyCollection<Vertegenwoordiger>.Empty'. Use the new keyword if hiding was intended.

'Werkingsgebieden.Empty' hides inherited member 'ReadOnlyCollection<Werkingsgebied>.Empty'. Use the new keyword if hiding was intended.