Duende IdentityServer - USers in Role throws error

Question

Just trying to get a list of the Users in a specific Role -

  var users = await _userManager.GetUsersInRoleAsync("Administrators");  

   return null;  

Throws

System.NotSupportedException: Serialization and deserialization of 'System.Action' instances are not supported. Path: $.MoveNextAction.

---> System.NotSupportedException: Serialization and deserialization of 'System.Action' instances are not supported.

Answer 1

No one? Surely this is a straightforward query to make.