From 088466da5c5305b01bf55ec30d48d739f9ab93d1 Mon Sep 17 00:00:00 2001
From: Massimiliano Galli <massimiliano.galli@cern.ch>
Date: Mon, 31 Mar 2025 15:07:00 +0200
Subject: [PATCH] [RF] Fix implementation of HS3 importers

Fix by @guitargeek.
The RooWSFactoryTool expression handler was not correctly matching branckets, leading to failures when importing
valid JSON filed with RooProdPdf objects.
---
 roofit/hs3/src/RooJSONFactoryWSTool.cxx | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/roofit/hs3/src/RooJSONFactoryWSTool.cxx b/roofit/hs3/src/RooJSONFactoryWSTool.cxx
index 8d047d6afe6dd..3489b0c5b7e98 100644
--- a/roofit/hs3/src/RooJSONFactoryWSTool.cxx
+++ b/roofit/hs3/src/RooJSONFactoryWSTool.cxx
@@ -370,8 +370,9 @@ std::string generate(const RooFit::JSONIO::ImportExpression &ex, const JSONNode
          RooJSONFactoryWSTool::error(errMsg.str());
       } else if (p[k].is_seq()) {
          bool firstInner = true;
+         expression << "{";
          for (RooAbsArg *arg : tool->requestArgList<RooAbsReal>(p, k)) {
-            expression << (firstInner ? "{" : ",") << arg->GetName();
+            expression << (firstInner ? "" : ",") << arg->GetName();
             firstInner = false;
          }
          expression << "}";