PartialResultToken is always `null`

I tried to stream workspace symbols and faced a problem that request.PartialResultToken and request.WorkDoneToken are always null. It is reproduced on the sample client/server from this repository and also on my small example:

class WorkspaceSymbolsHandler : WorkspaceSymbolsHandlerBase
{
      public override Task<Container<SymbolInformation>> Handle(WorkspaceSymbolParams request, CancellationToken cancellationToken)
      {
         Debug.Assert(request.PartialResultToken != null); // always false
         Debug.Assert(request.WorkDoneToken != null); // always false

         var location = new Location(){
               Uri = "test.uuu",
               Range = new Range(0, 0, 1, 1)
         };

         var symbols = new List<SymbolInformation>() {
               new SymbolInformation{ Name = "Symbol-1", Location = location},
               new SymbolInformation{ Name = "Symbol-2", Location = location},
               new SymbolInformation{ Name = "Symbol-3", Location = location},
         };

         return Task.FromResult<Container<SymbolInformation>>(symbols);
      }

   protected override WorkspaceSymbolRegistrationOptions CreateRegistrationOptions(WorkspaceSymbolCapability capability, ClientCapabilities clientCapabilities)
   {
      return new(){ WorkDoneProgress = true };
   }
}

Do I have to do something else on the client or on the server to get a token?

Start with the sample client/server mentioned in the report and trace the WorkspaceSymbolsHandler request shown in the reproduction. Compare how PartialResultToken and WorkDoneToken are sent and deserialized, then verify the expected token behavior with the sample or linked example; done means the cause and required client/server change are demonstrated.