The PaginationOptions is the class from arg 0 of https://github.com/jclouds/jclouds-labs-openstack/blob/master/openstack-neutron/src/main/java/org/jclouds/openstack/neutron/v2_0/features/NetworkApi.java#L90 This cast will always succeed because it's baked right into the code. Object is the correct argument as it's what's required by the base abstract class Arg0ToPagedIterable. No need to checkArgument.