Roofit upper limit unstable for negative pdf (with AsymptoticCalculator)

Roofit and RooStats
14

Hi @StephanH,
This sounds very nice! But… how can I use that within the AsymptoticCalculator machinery?
The minimal lines of interest should be the following:

    ac = ROOT.RooStats.AsymptoticCalculator(dh_bg, b_modelNM, sb_modelNM)
    ac.SetOneSided(True)
    ROOT.RooStats.AsymptoticCalculator.SetPrintLevel(-1)
    asympResult = ac.GetHypoTest()
    calc = ROOT.RooStats.HypoTestInverter(ac)
    calc.SetVerbose(False)
    calc.SetConfidenceLevel(0.95)
    calc.UseCLs(True)
    profll.SetOneSided(True)
    calc.SetFixedScan(npoints, poimin, poimax)
    r = calc.GetInterval()
    upperLimit = r.UpperLimit()

I have found no documentation showing how to use the EvalErrorWall within an Upper Limit calculator like the AsymptoticCalculator.
Many thanks.