There are a number of places which use something like:

InstanceIdentifier.builder(NetworkTopology.class)
            .child(Topology.class, new TopologyKey(new TopologyId("someName")))
            .build() 

The here the result of build() results in InstanceIdentifier<Topology>, whereas we statically know it results in KeyedInstanceIdentifier<Topology, TopologyKey>.

Provide an specialization of InstanceIdentifierBuilder, whose build() method results in KeyedInstanceIdentifier and return that builder from keyed child() methods.