@Override
    public void addCategory(String id) {
      // read only, nothing to do
    }
Only to be used when replaying persisted requests upon server startup.

@param requestId    logical request id
@param id           host request id
@param predicate    host predicate
@param topology     cluster topology
@param entity       host request entity
ambari-server/src/main/java/org/apache/ambari/server/topology/HostRequest.java