Add Warning to ParamHistFunc Compatibility

Author: Phmonski

roofit/hs3/src/JSONFactories_RooFitCore.cxx

@@ -540,6 +540,14 @@ class ParamHistFuncFactory : public RooFit::JSONIO::Importer {
    {
       std::string name(RooJSONFactoryWSTool::name(p));
       RooArgList varList = tool->requestArgList<RooRealVar>(p, "variables");
+      if (!p.has_child("axes")) {
+         std::stringstream ss;
+         ss << "No axes given in '" << name << "'" 
+            << ". Using default binning (uniform; nbins=100). If needed, export the Workspace with a newer Root version that supports histogram binnings(>6.37.01)." << std::endl;      
+         RooJSONFactoryWSTool::warning(ss.str());
+         tool->wsEmplace<ParamHistFunc>(name, varList, tool->requestArgList<RooAbsReal>(p, "parameters"));
+         return true;
+      }
       tool->wsEmplace<ParamHistFunc>(name, readBinning(p, varList), tool->requestArgList<RooAbsReal>(p, "parameters"));
       return true;
    }