multi: Send empty VSP policy fields

This changes the call sites of VSP library functions to fill in missing
policy choices with empty maps instead of nil maps.

This fixes an issue where certain VSPs will fail to accept the policy
calls because those fields are required by the API but not sent.

internal/rpc/jsonrpc/methods.go

@@ -3829,7 +3829,9 @@ func (s *Server) setTreasuryPolicy(ctx context.Context, icmd any) (any, error) {
 	policyMap := map[string]string{
 		cmd.Key: cmd.Policy,
 	}
-	err = s.updateVSPVoteChoices(ctx, w, ticketHash, nil, nil, policyMap)
+	choices := map[string]string{}
+	tspendPolicy := map[string]string{}
+	err = s.updateVSPVoteChoices(ctx, w, ticketHash, choices, tspendPolicy, policyMap)
 
 	return nil, err
 }
@@ -3963,7 +3965,9 @@ func (s *Server) setTSpendPolicy(ctx context.Context, icmd any) (any, error) {
 	policyMap := map[string]string{
 		cmd.Hash: cmd.Policy,
 	}
-	err = s.updateVSPVoteChoices(ctx, w, ticketHash, nil, policyMap, nil)
+	choices := map[string]string{}
+	treasuryPolicy := map[string]string{}
+	err = s.updateVSPVoteChoices(ctx, w, ticketHash, choices, policyMap, treasuryPolicy)
 	return nil, err
 }
 
@@ -4680,7 +4684,9 @@ func (s *Server) setVoteChoice(ctx context.Context, icmd any) (any, error) {
 	}
 
 	// Update voting preferences on VSPs if required.
-	err = s.updateVSPVoteChoices(ctx, w, ticketHash, choice, nil, nil)
+	tspendPolicy := map[string]string{}
+	treasuryPolicy := map[string]string{}
+	err = s.updateVSPVoteChoices(ctx, w, ticketHash, choice, tspendPolicy, treasuryPolicy)
 	return nil, err
 }
 

wallet/wallet.go

@@ -408,7 +408,7 @@ func (w *Wallet) AgendaChoices(ctx context.Context, ticketHash *chainhash.Hash)
 	const op errors.Op = "wallet.AgendaChoices"
 	version, deployments := CurrentAgendas(w.chainParams)
 	if len(deployments) == 0 {
-		return nil, 0, nil
+		return map[string]string{}, 0, nil
 	}
 
 	choices = make(map[string]string, len(deployments))