@Override
  public CompletableFuture<List<NamespaceDescriptor>> listNamespaceDescriptors() {
    return this.<List<NamespaceDescriptor>> newMasterCaller()
      .action((controller, stub) -> this.<ListNamespaceDescriptorsRequest,
        ListNamespaceDescriptorsResponse, List<NamespaceDescriptor>> call(controller, stub,
          ListNamespaceDescriptorsRequest.newBuilder().build(),
          (s, c, req, done) -> s.listNamespaceDescriptors(c, req, done),
          (resp) -> ProtobufUtil.toNamespaceDescriptorList(resp)))
      .call();
  }
Utility for completing passed TableState {@link CompletableFuture} <code>future</code> using
passed parameters. Sets error or boolean result ('true' if table matches the passed-in
targetState).
hbase-client/src/main/java/org/apache/hadoop/hbase/client/RawAsyncHBaseAdmin.java